LiDAR Quality Assurance (QA) Report Sabine/Shelby Counties - Texas Prepared for Texas Water Development Board March 14, Submitted to: TWDB

Transcription

1 LiDAR Quality Assurance (QA) Report Sabine/Shelby Counties - Texas Prepared for Texas Water Development Board March 14, 2012 Submitted to: TWDB Prepared by:

2 Table of Contents 1 Executive Summary LiDAR Quantitative Review LiDAR Completeness Review... 7 LAS Extents LiDAR Qualitative Review Artifacts Divots Divot Display Issues Flight Line Ridges / Noise Misclassifications Data Voids LiDAR Recommendation Breakline Analysis Breakline Data Overview Insufficient Breakline Vertices Breakline Overlap Breakline Capture Issues Breakline Should be Removed Water Not Captured Breaklines Should be Adjusted Breakline Should Split at Culvert Topology Monotonicity Errors Breakline Quantitative Review Breakline Recommendation Hydro-enforced Digital Elevation Model Analysis Qualitative Review DEM Does Not Display DEM Edge Tinning DEM Tiling DEM Edge Rounding Missing Pixels Misclassification in DEM Divots in DEM Hydro Enforcement Review Floating Water Digging Water Water Artifacts Intensity Images Metadata GDB Recommendation Summary... 36

3 1 Executive Summary Contract: TWDB: Sabine/Shelby Counties, TX Production Contractor: GeoEye Date Prepared: 3/14/2012 Delivery #: 2 Dewberry Recommendation: Return for Corrections Data History: 1st delivery Sept, nd delivery pilot Nov, nd delivery full datasets Feb, The following QA/QC report documents Dewberry s second review of the LiDAR and first full review of the additional deliverables for Sabine and Shelby Counties, Texas. The project area covers approximately 1,110 square miles and is divided into 433 tiles. The Sabine/Shelby data has undergone significant improvements for the second delivery, however errors remain which cause Dewberry to recommend the LiDAR, breaklines, and DEMs be returned for further corrections. LiDAR This is the second review of the LiDAR for Sabine/Shelby, TX. As stated in the first review quality assurance report, the LiDAR passes vertical accuracy specifications. The data has an RMSE Z in open terrain of 10.9 cm which meets the v13 USGS specifications. The fundamental vertical accuracy is 21.4 cm which meets the project specification of 24.5 cm. In addition, TWDB has an additional requirement that the points in Forest need to meet an RMSE of 25cm which they do at 23.8 cm. Several issues were identified in the first delivery LiDAR quantitative review including large portions of tiles that were not fully classified, several very high or very low points classified as ground, artifacts, divots and misclassifications. Nearly all calls placed the during the first delivery LiDAR review were appropriately addressed for the second delivery. A small number of new LiDAR calls have been placed, mainly for tiles that could not be fully reviewed at the micro level during the first delivery. Dewberry recommends all new and remaining LiDAR calls receive further corrections. These include: Two data voids in the second delivery that were not present in the first delivery. LAS header record errors including missing projection information, GPS timestamp record errors, sensor scan angle record errors and points in extraneous classes. Tiling that varies slightly from the required USGS 1/16 th quadrangle system. Remaining quality issues including one extreme noise point classified as ground, one flight line ridge, artifacts, divots and misclassifications Additionally, Dewberry has become aware that the Sabine/Shelby data may contain divots which are undetectable using standard QA/QC procedures. These divots consist of only single points, usually located within topographically varied terrain. Unlike typical divots, these divots do not display in LiDAR ground models or in DEMs. We made all reasonable efforts find divots of this type, however further measures that are outside of our specified QA/QC process would be needed to ensure all divots with display issues are detected. Breaklines This is the second review of the Sabine/Shelby breaklines, however because the first review was done before the hydroflattened DEMs were available, this review included additional steps and is more

4 comprehensive than the first. The breaklines contain errors and inconsistencies, and are being recommended for further corrections. Errors include: DEMs An insufficient number of breakline vertices which causes detail loss. This affects approximately one half of the project area, and makes for an inconsistent data set. Breaklines which need to be removed because they capture ground or mostly ground rather than water. Breaklines which need horizontal placement adjustments to better capture the actual land/water interface as it appears at the time of data collection. File structure issues including missing projection information and combined delivery of all breaklines into one feature class rather than separating by type (Ponds, Drainage, Islands). Monotonicity errors; the breakline z values must be flat or uniformly sloping downhill. This is the first review of the Digital Elevation Models (DEMs) for Sabine/Shelby, TX. We recommend the DEMs be returned for further corrections. DEMs are a final product created from the LiDAR and breaklines, meaning all errors called as needing corrections in this LiDAR and Breakline review also apply to the DEMs. Additional DEM errors are summarized here: Two DEMs are missing all elevation data and cannot be reviewed. DEMs located on the edge of the project contain edge errors including extents that do not match that of the LiDAR and tinned edge artifacts. DEM tiling varies from the USGS 1/16 th quadrangle system. Numerous cases of floating water were identified. Some cases of water artifacts and digging water identified. 1.1 LiDAR Quantitative Review One of the first steps in assessing the quality of the LiDAR is a vertical accuracy analysis of the ground models in comparison to surveyed checkpoints. This analysis was run of the first delivery LiDAR and because of checkpoint locations, did not need to be rerun on the second delivery LiDAR. The analysis as it appears in Dewberry s first delivery QA/QC report is reproduced here: We surveyed sixty seven (67) checkpoints for the entire project area extent. Sixty four (64) checkpoints were used to calculate the vertical accuracy. Three points were removed from the vertical accuracy testing and the reasoning behind this is discussed below.

5 Figure 1 Checkpoints distribution for Sabine/Shelby Counties, TX The vertical accuracy assessment compares the measured survey checkpoint elevations with those of the TIN as generated from the bare-earth LiDAR. The X/Y locations of the survey checkpoints are overlaid on the TIN and the interpolated Z values of the LiDAR are recorded. These interpolated Z values are then compared with the survey checkpoint Z values and this difference represents the amount of error between the measurements. Once the Z values are recorded, the Root Mean Square Error (RMSE) is calculated and the vertical accuracy scores are interpolated from the RMSE value. The RMSE equals the square root of the average of the set of squared differences between the dataset coordinate values and the coordinate values from the survey checkpoints. The first method of evaluating vertical accuracy uses the FEMA specification which follows the methodology set forth by the National Standard for Spatial Data Accuracy. The accuracy is reported at the 95% confidence level using the Root Mean Square Error (RMSE) which is valid when errors follow a normal distribution. By this method, vertical accuracy at the 95% confidence level equals RMSE Z x The second method of testing vertical accuracy, endorsed by the National Digital Elevation Program (NDEP) and American Society for Photogrammetry and Remote Sensing (ASPRS) uses the same (RMSEZ x ) method in open terrain only; an alternative method uses the 95th percentile to report vertical accuracy in each of the other land cover categories (defined as Supplemental Vertical Accuracy

6 SVA) and all land cover categories combined (defined as Consolidated Vertical Accuracy CVA). The 95th percentile method is used when vertical errors may not follow a normal error distribution, as in vegetated terrain. The Fundamental Vertical Accuracy (FVA) is calculated in the same way when implementing FEMA/NSSDA and NDEP/ASPRS methodologies; both methods utilize the 95% confidence level (RMSEZ x ) in open terrain where there is no reason for LiDAR errors to depart from a normal error distribution. After the analysis was run, three points were removed: OT-43, GWC-11, and GWC-33. OT-43 is a point in open-terrain, but when the LiDAR was collected the field contained high grass. In addition the point is terrain where the slope is undulating and this creates issues when calculating that RMSE. Points GWC- 11 and GWC-33 are points in high grass/weeds/crops and both these points are located on or near a bank at the side of the road. Survey check points cannot be used if there is a significant change in slope near the point as is the case in both these points. After removing these points there are still over 60 checkpoints for the area and the data meets project specifications for vertical accuracy. Table 1 outlines the calculated RMSEz and associated statistics in feet while Table 2 outlines vertical accuracy and the statistics of the associated errors as computed by the different methods in feet. 100 % of Totals RMSE Z (m) Spec=0.125 m 1 Mean (m) Median (m) Skew Std Dev (m) # of Points Min (m) Max (m) Consolidated Open Terrain High Grass Forest Urban Table 1: The table shows the calculated RMSEz values in meters as well as associated statistics of the errors for Sabine/Shelby, Texas. 1 In open terrain. Land Cover Category # of Points FVA Fundamental Vertical Accuracy (RMSE Z x ) Spec=0.245m CVA Consolidated Vertical Accuracy (95th Percentile) Spec=0.363m SVA Supplemental Vertical Accuracy (95th Percentile) Spec=0.363m Consolidated Open Terrain High Grass Forest Urban Table 2: The table shows the calculated Accuracy z of the FVA in meters using FEMA/NSSDA guidelines (RMSEz x ) and the Accuracy z of the CVA in meters using NDEP/ASPRS guidelines (95 th percentile) for Sabine/Shelby, Texas. The data delivered for Sabine/Shelby, TX has an RMSE Z in open terrain of 10.9 cm which meets the v13 USGS specifications. The fundamental vertical accuracy is 21.4 cm which meets the project specification of 24.5 cm. In addition, TWDB has an additional requirement that the points in Forest need to meet an RMSE of 25cm which they do at 23.8 cm. Dewberry identifies no issues with the vertical accuracy as delivered for Sabine/Shelby Counties, TX.

7 1.2 LiDAR Completeness Review Dewberry received four hundred and thirty three (433) LiDAR tiles in the second delivery. The Point Data Format 1 is used, with intensity values present. The LAS files are named appropriately according to the USGS quarter quarter quad system and have correct extents (1.875 minute x minute). The following errors exist in the second delivery LiDAR header records: 1. Missing projection information in the header record of all tiles. Projection should be listed as follows: Vertical Datum: NAVD88, Geoid03 Projection: NAD 1983 UTM Zone 15N Horizontal and Vertical Units: Meters 2. The minimum and maximum GPS timestamps are recorded incorrectly for two hundred and forty two (242) tiles. These tiles are listed in a Microsoft Excel spreadsheet file accompanying this document. 3. The minimum and maximum scan angles for most tiles exceed the target specification of plus or minus 20 degrees off nadir. Dewberry has examined 100% of the tiles for flight line ridges, noise and other anomalies that may be caused by higher than recommended scan angles. One flight line ridge was detected and is discussed below. Otherwise, Dewberry concludes the high scan angles do not adversely impact the ground model. 4. Additionally, there are several anomalous scan angles which are greater than plus or minus 100 degrees from nadir. These appear to be a documentation error in the header record of several tiles. A list of tiles with anomalous scan angles is provided in a Microsoft Excel spreadsheet accompanying this document. 5. The LiDAR contains many extraneous classes. According to the project scope of work, the LiDAR classification should include classes 1 unclassified 2 ground 6 buildings 7 noise 9 water 13 bridges The LiDAR currently contain these additional classes: 0, 3, 4, 5, 11, 12, 13, 15, 16, 17, 21, 22, and 26. Points in the extraneous classes should be reclassified. A list of tiles containing incorrect classes is provided in a Microsoft Excel spreadsheet accompanying this document LAS Extents The scope of work requires the LiDAR be tiled according to the USGS 1/16 th quadrangle system. The actual LAS vary slightly from this in places. Some tiles do not seem affected while other vary from the USGS tile grid by over a meter.

8 Figure 2 LAS tile u319341_1_a_la displayed as an ESRI masspoint with the USGS 1/16 th quadrangle tile scheme in black. The LAS extent matches the quarter quarter quad system at its western edge but varies from it by about 1 meter in its northern extent. 1.3 LiDAR Qualitative Review Dewberry performed a 100% micro level inspection of the first delivery LiDAR. The goal of Dewberry s qualitative review is to assess the continuity and the level of cleanliness of the bare earth product. Each LiDAR tile is expected to meet the following acceptance criteria: The point density is homogenous and sufficient to meet the user s needs; The ground points have been correctly classified (no man-made structures or vegetation remains, no gaps except over water bodies); The ground surface model exhibits a correct definition (no aggressive classification, no oversmoothing, no inconsistency in the post-processing); No obvious anomalies due to sensor malfunction or systematic processing artifacts are present (data voids, spikes, divots, ridges between flight lines or tiles, cornrows, etc); Residual artifacts <5%. Two large issues were noted including during the first delivery review including fifty eight (58) tiles that were not fully classified and one hundred and sixty three (163) tiles that contained very high or very low points classified as ground. All tiles are now fully classified; one tile remains that has a very high point, listed here: Table 3 Tile in the second delivery that contains a high point. Tile Outlier Z value (m) u319341_1_c_la

9 In the first delivery, these extreme noise points sometimes caused display issues with the bare earth models used in the QA process, meaning the tiles could not be fully reviewed at the micro level. For the second delivery, any tiles with display issues as well as the fifty eight (58) tiles with major classification issues were closely reviewed in full. For this reason, a limited amount of new LiDAR calls are made in this second delivery review. Additionally, many quality review calls were made for the first delivery LiDAR including artifacts, misclassification, divots, water classification issues, and one flight line ridge. For the second delivery, Dewberry assured that all first delivery edit calls had been addressed by the LiDAR provider. In most cases this means the call was fixed by GeoEye. In some cases this means that GeoEye and Dewberry were able to determine using the Digital Elevation Models (DEMs), which were not available during the first delivery LiDAR review, that the call does not significantly impact the DEM. Table 4 LiDAR QA calls for Second Delivery Sabine/Shelby Counties, Texas Issue First Delivery Number of Occurrences Number of Remaining Issues Artifacts - Bridge 13 0 Artifacts Misclassification 3 0 Artifacts - Structure 6 2 Artifacts Vegetation Divot Flight Line Ridge (number of calls caused by single ridge) Misclassification Misclassification Aggressive Classification 18 0 Misclassification Culvert 9 0 Misclassification Soil Mounds (Inconsistent Editing) 5 2 Misclassification Water 3 2 Misclassification Break Line 13 4 Unclassified Entire Tiles 58 0 Data void 0 2 TOTAL Artifacts Artifacts are points returned from vegetation or structures that are mistakenly classified as ground points. Most artifacts have been removed by GeoEye for the second delivery. A small amount of vegetation and partial structure artifacts remain. The residual artifacts make up less than 2%.

10 Figure 3 Bare earth model of second delivery tile u319343_3_c_la showing a vegetation artifact. The artifact measures approximately 7 m in height. This artifact should be removed from the bare earth LiDAR Divots When LiDAR is collected the sensor will sometimes will return noise points that are considerably lower than the surrounding points. During classification, these low points may be classified to ground. If these points are not manually removed, a divot will be present in the ground model. Dewberry detected seventeen (17) divots remaining in the second delivery Sabine/Shelby LAS. Dewberry recommends these be corrected.

11 Figure 4 Bare earth model of second delivery tile u319351_1_c_la showing 90 m divot. The low point causing the divot should be classified to class 7, noise Divot Display Issues A problem has emerged in the Sabine and Shelby LiDAR concerning divots that are undetectable by ordinary QA/QC procedures. Some divots consisting of single points among varied terrain do not display in normal bare earth elevation models. An ESRI terrain was built for tile u319415_4_c_la using all class 2 LAS points. The terrain was used to check the vertical placement of a water body located in the tile. However, while viewing the terrain Dewberry analysts detected a divot that had not been visible in the typical LiDAR and DEM QA/QC software. Figure 5 shows the divot as it is seen in the terrain and as it appears in a profile of the LAS points. The profile confirms that the divot is classified into class 2, ground. Figure 6 shows the same area as it appears in a bare earth elevation model created using Quick Terrain Modeler, an industry standard LiDAR visualization software package used extensively by Dewberry during the QA/QC process. Though the divot exists, it is not detectable in the model. Figure 6 also shows the DEM of the same area as it appears in another typical LiDAR software package, Global Mapper. Again, though the divot exits in the DEM, it is not able to be interpreted and displayed by the modeling software and is therefore undetectable. Dewberry used all reasonable measures to detect any divots that were initially missed due to these model display issues. This included looking at tile statistics for low points and examining tiles for which a terrain was readily available. Nine divots were detected in this way. Dewberry does not guarantee that every divot which has display issues was detected in this second review; divots with display issues are in the range of 40 to 80 m below the surrounding terrain. This range is possibly within the natural topographic variance expected within the tile containing the divot. This means the divot will not be detected as a low point for all tiles. Dewberry is willing to perform a more extensive search for divots with display issues. This could be done either by creating a tool which detects local outlying ground points or by creating a terrain of the full project area expressly for the purpose of detecting divots. Both these solutions are processing intensive and, due to the large size of the project area, would require several days to complete. This task is also outside the standard QA procedure agreed on in the task order for this project. TWDB should evaluate the issue of divots with display problems, and communicate with Dewberry as to the best course of action for proceeding.

12 Figure 5 A 50 m divot that was identified in an ESRI bare earth terrain. (Left) An LAS profile of the divot confirms that the low point is classified as ground. Ground points are displayed in pink. (Right) Figure 6 Ground elevation model of second delivery LAS tile u319415_4_c_la as is displays in the software package Quick Terrain Modeler. The divot that is known to exist does not display. (Left) Also pictured is the DEM of tile u319415_4_c as it displays in the software package Global Mapper. Again, though the divot is present in the DEM, it is undetectable in the model. (Right) Flight Line Ridges / Noise Flight line ridges and flight line noise occur where one flight line s elevation values do not match another flight line s elevation values. This is generally due to poor calibration during post-processing. All flight line ridge and noise calls made by Dewberry in the first delivery were adequately corrected by GeoEye in the second delivery. However, in the centrally located area which was not fully classified for the first delivery one new flight line ridge was detected. The ridge measures 20 to 35 cm and should be corrected.

13 Figure 7 The flight line ridge at its northernmost end as seen in the ground elevation model of second delivery tile u319359_1_b_la. The ridge averages about 30 cm. Figure 8 Full point cloud profile of second delivery LAS tile u319359_1_b_la showing the flight line ridge where three flight lines overlap. The profile is colored by flight line source identification number. Notice that the dark blue and yellow flight lines match well vertically, but the flight line shown in purple is offset Misclassifications A small number of misclassifications remain in the second delivery Sabine/Shelby LiDAR. Misclassification calls named only mis imply that LiDAR points are unclassified when they should be

14 classified to ground. Misclassifications calls that specify water to ground in the call name imply that points currently classified as water should be moved to class 2, ground. Figure 9 Ground density model of second delivery LAS tile u319335_3_c_la showing an area of misclassification. Figure 10 Full point cloud intensity model of LAS tile u319335_3_c_la showing the same misclassified area. There is no apparent reason the area shown in red in the density model above should not be included in ground.

15 Figure 7 Ground density model of second delivery LAS tile u309335_1_b_la showing a river with the project breaklines overlaid in blue. A large riverbank has been correctly excluded from the river breakline, but has not been classified into class 2, ground. It appears red in the ground density model. Figure 8 - Figure 10 Full point cloud intensity model of LAS tile u309335_1_b_la showing the same river bank. The intensity image confirms that the area is ground, not water.

16 Figure 9 LAS points from second delivery tile u309335_1_b_la colored by classification where pink points are ground, yellow points are unclassified, and blue points are water. The area identified above is misclassified as water Data Voids Two data voids appeared in the second delivery Sabine/Shelby LiDAR. The voids are several acres in area and are located in tiles u319318_1_b_la and u309327_1_b_la. Both data voids were not present in the first delivery, meaning the data does exist. The voids should be corrected. Figure 10 Second delivery LAS tile u319318_1_b_la colored by elevation. A data void of approximately 11 acres has appeared in the second delivery tile.

17 Figure 11 First delivery LAS tile u319318_1_b_la colored by elevation. All points are present; there is no data void. 1.4 LiDAR Recommendation Dewberry recommends the second delivery Sabine/Shelby LiDAR be returned for further corrections. The two data voids and the tile with excessive high or low points must be corrected. The tiles should be correctly tiled to the USGS 1/16 th quadrangle system without variations. The flight line ridge, divot calls, misclassifications and artifacts should be corrected. A GDB containing all LiDAR edit calls is provided with this report. Calls identified as Fixed need no further action. Calls identified as Not fixed or New Call make up all remaining issues. Additionally, TWDB should evaluate the issue of divots that require non-standard procedures to detect, and should communicate with Dewberry as to whether further action is desired. 2 Breakline Analysis A qualitative/quantitative review was completed on the first delivery breaklines. The qualitative review consisted of a visual review of the breaklines for: 1) Compilation completeness, 2) Horizontal placement accuracy, and 3) Proper feature coding. This visual analysis was followed by several automated tests for hydro-enforcement and topology using ESRI PLTS tools and proprietary tools developed by Dewberry. Thirty four (34) breakline quality calls as well as several hydro enforcement calls were made on the first delivery breaklines. All topology calls and several (but not all) visual breakline calls were corrected by GeoEye for the second delivery breaklines. However, major errors remain in the second delivery breaklines. For the second Sabine/Shelby review, in addition to the breaklines Dewberry received the hydro flattened DEMs. Thus the second delivery breakline review was more comprehensive than the first. Some overall inconsistencies and other errors were detected. These include widespread loss of detail due to an insufficient number of breakline vertices, general structure problems, overlap for nearly all island features and breakline placement issues. Additionally, altering breaklines introduces the possibility of creating new errors. For this reason

18 all automated checks were re-run on the second delivery breaklines and a small number of errors were returned from these. 2.1 Breakline Data Overview The breaklines as delivered to Dewberry were contained in a single, 3-D shapefile. The breaklines shapefile contains 3 records; ponds, islands, and drainage. Each record was a continuous layer of a specific breakline, which adheres to project specifications. For clarity and ease of use, Dewberry recommends the more standard method of breakline delivery is followed by separating the breaklines into three separate shapefiles Ponds, Islands and Drainage. The breakline shapefile had no accompanying.prj file, which results in the breaklines not being projected. This is an issue that needs to be addressed. Figure 12 The projection information for the delivered breakline shapefile has not been defined. 2.2 Insufficient Breakline Vertices During our second delivery breakline review we identified an insufficient number of vertices used to define the breaklines for a large amount of the project area. This affects the quality and aesthetics of the breaklines, LiDAR and DEMs. It also creates an inconsistent data set, since portions of the breaklines model the water features correctly and sufficiently. The issue is too widespread to be marked at every location; however we identified the affected area using a polygon shapefile as seen in Figure 13. Our recommendation is that the data provider review the identified section and add vertices to areas appearing rough or jagged. This should be done at a scale that is appropriate to the detail level of the water features. TWDB should examine the examples provided below and determine if our recommendation is the best course of actions for their needs.

19 Figure 13 Map of the Sabine/Shelby project area with the breaklines shown in blue. Highlighted in red is the area in which breaklines with insufficient vertices were identified. The area should be reviewed and corrected.

20 Figure 14 Full point intensity image with breaklines shown in green. The breaklines do not contain enough vertices to accurately model the land/water interface. Figure 15 A second example of breaklines with drawn with an insufficient number of vertices from the intensity image of tile u319342_4_b_in. This example is shown at twice the scale of the previous example, showing that the issue is great enough to be seen even at larger zoom levels.

21 Figure 16 DEM tile u319342_4_b showing the same area as seen in Figure 15. The rough breaklines have a visible impact on the DEMs, making the islands and shoreline appear jagged. Figure 17 The effect of rough breaklines affecting DEM tile u309312_1_b. The islands and shoreline have lost detail due to insufficient vertices in the breaklines.

22 2.3 Breakline Overlap The islands breakline has not been removed from the ponds and drainage breakline. Instead, the islands are overlaid as another polygon, which causes duplicate geometry and errors when calculating size of the water feature breaklines. The island should be erased from the pond and drainage polygons to form a complete, non-overlapping breakline dataset. No makers are placed since nearly every island has this issue. An example can be seen below. When fixing this error, the data provider should be aware that a small number of donut captures are present in which a lake exists inside an island. In these cases, the interior lakes must also be erased from the islands. Figure 18 Full point cloud intensity image of tiles u319351_2_a_in and u319351_2_b_in. The island breakline is outlined in green with a hollow fill. The pond breakline has a blue fill. There is no break in the pond breakline where the island exists. This can lead to false geography. 2.4 Breakline Capture Issues General inconsistencies were noted during the second delivery breakline review. Because of this, a 100% visual review was conducted on the breaklines. Capture errors remain which should be addressed. A geodatabase documenting the edit calls is provided with this document Breakline Should be Removed Twenty five (25) calls were made for breaklines that should be removed from the breaklines shapefile. These calls were made on pond breaklines that are either not capturing any water, or are capturing small amounts of water (less than 2 acres) and much surrounding ground.

23 Figure 19 Full point cloud intensity image of tile u309320_1_a_in. A pond breakline has been drawn around an area containing no water. The breakline should be removed. 2.5 Water Not Captured Two (2) calls were for water bodies over two acres that are not captured. Both connect several drainage features. The drainage breakline should be extended to include the two areas. Figure 20 Tile u319301_4_d_in showing a portion of a water body that is not captured by the breaklines. The water exceeds two acres and connects several other features. It should be included in the breaklines.

24 2.6 Breaklines Should be Adjusted This call was generally made for areas where ground has been captured as water by the breaklines. For the first delivery breakline review, Dewberry made the general comment that river banks had been treated inconsistently throughout the project. This issue was not addressed in the second delivery breaklines. Thus for the second review, Dewberry analysts placed a call on every river bank that had been incorrectly captured as water. Streams should be captured consistently and accurately and should not include sandy banks. The river capture should look like that in Figure 22. Additionally, some adjustments need to be made to the pond and drainage breaklines. The breaklines should only capture water present at the time of the LiDAR collection and therefore visible as water in the intensity images. As they are now, some breaklines capture large portions of bank that may sometimes be flooded but are land at the time collection. A total of 172 breakline adjustment calls were made. The large majority of these are riverbanks. The images below provide examples of inconsistent riverbank collection (Figure 21 and Figure 22Figure 23) and incorrect water body collection (Figure 23). Figure 21 Full point cloud intensity image of tile u319360_4_c_in in the northern portion of the dataset. The drainage breakline incorrectly encompasses the banks around the bends.

25 Figure 22 Full point cloud intensity image of tile u309335_3_c_in in the southern portion of the dataset. The drainage breakline here is correctly captured around the banks. Figure 23 Full point cloud intensity image of tile u319318_3_c_in. The breakline extends far past the actual bounds of the water. Breaklines should only capture water present at the time of LiDAR collection Breakline Should Split at Culvert One area was identified where a culvert has been correctly classified to ground for the second delivery, however the breakline has not been updated to account for the culvert. The pond breakline (north) can remain as it is, however the drainage section of the breakline (south) should be moved downward so it no longer includes the culvert.

26 Figure 24 Tile u19352_3_b_in. The breakline is capturing a culvert which has been classified to ground. It should split around the culvert. This area is pictured again in the DEM section of this report. 2.7 Topology One of the requirements of hydro breaklines is valid topology. Dewberry tested the topology using ESRI s PLTS extension and proprietary tools to ensure that the breaklines are not overlapping, that all water bodies are flat within a tolerance, and that all breaklines have elevations defined. These data checks allow automated validation of 100% of the data. In order to perform the topologic tests, the breaklines shapefile was broken up into three different shapefiles, one for each type of breakline. Then these three shapefiles were projected based on the projected specifications since they did not come with a defined projection. The breaklines passed all PLTS checks except the following: Polygon Overlap Check o This issue was also discussed in the Breakline Overlap section above. The topology tool returns features whose breaklines overlap with an existing breakline. Over 600 results were returned because the island breaklines have not yet been erased from the pond and drainage breaklines. Geometry on Geometry Check o This tool was set to check for areas where breakline outlines cross one another. One result was returned. It appears that this island feature was accidently shifted slightly upward making its breakline cross the drainage feature in which it exists. The island placement should be corrected Monotonicity Errors A stream is monotonic when all its verities are flat or uniformly sloping in one direction. Monotonicity errors were found using both an automated tool and during the visual review of the hydro-enforced DEMs. A total of twenty six (26) monotonicity calls were made. These should be corrected.

27 2.8 Breakline Quantitative Review The quantitative vertical analysis compares breakline vertex elevations against the bare-earth LiDAR data. To do this, the breaklines are converted to points with Z values maintained as an attribute. An ESRI Terrain is created from the LiDAR using only ground points. The elevation of the LiDAR is derived by extracting the Z value of the terrain at the same X/Y values of the points. An analysis of the elevation comparison between the points and the terrain is conducted to assess the vertical placement of the breaklines. Several vertices were discovered that float above the terrain surface. These vertices have a direct and visible impact on the DEM. Floating water is not acceptable and should be corrected. Because floating and digging water is best viewed using the hydro enforced DEMs, floating water calls are included in the DEM edit call shapefile located in the geodatabase accompanying this review. Examples of floating water are given in the DEM section of this report. 2.9 Breakline Recommendation The breaklines should be returned for further edits. TWDB should review the issue of detail loss due to insufficient vertices and should communicate with Dewberry to decide the best course of action for this widespread issue. All breakline capture issues identified by Dewberry in the geodatabase accompanying this report should be corrected. This includes the inconsistent collection of riverbanks, also a widespread issue. The one crossing feature should be corrected. Once all capture issues are addressed, monotonicity errors (as well as floating and digging water, discussed further below) should be corrected. The islands should be removed from the drainage and pond breaklines forming one continuous, non-overlapping breakline dataset. Additionally, the breaklines should be separated into three separate feature classes (Islands, Ponds and Drainage) and should be projected according to project specifications. 3 Hydro-enforced Digital Elevation Model Analysis Dewberry received 433 DEMs. DEM naming convention is correct and all DEMs are projected according to project specifications, although the tiling scheme is slightly off from the USGS quarter quarter quad systems. DEMs are 1 meter spatial resolution as specified. Projection: NAD83 UTM Zone 15 North Horizontal and Vertical Units: Feet 3.1 Qualitative Review All DEMs were visually inspected for errors and anomalies. The review also includes an examination of water features to identify hydro flattening errors. Vertices identified as digging or floating in the vertical variance calculation of the breakline Z values are used to help direct attention to probable hydro flattening errors during the DEM review. Several errors were detected in the DEMs. These include two DEMs that do not display data, edge artifacts and extent errors for edge DEM tiles, missing pixels, water artifacts, digging water and floating water. Additionally, all LiDAR and breakline calls identified in the two previous sections are present in the DEMs.

28 3.1.1 DEM Does Not Display DEM tiles u319351_3_a and u319341_1_c are missing all elevation data and do not display. These DEMs need to be reprocessed for review. Figure 25 DEM u319351_3_a does not display DEM Edge Tinning The DEM edges are incorrectly processed and introduce tinning along the outer edges of the project. The DEMs should be processed to the USGS quarter quarter quad tiling system without creating these edge errors. Figure 26 An example of a tinned edge artifact introduced in the processing of the DEMs. This issue should be corrected. Tile lu309319_4_b.

29 3.1.3 DEM Tiling In addition to the edge errors, DEM extents do not precisely match that of the USGS quarter quarter quad system. The DEMs vary by 5 meters up to about 40 meters. This means they also do not match the LiDAR extents. Figure 27 Two DEM edges are shown with the USGS 1/16 th quadrangle tiling scheme in shown in black. The DEMs do not exactly match the USGS quarter quarter quad tiling system DEM Edge Rounding DEMs on the edge of the project boundary have rounded corners in comparison to the LAS extents. This is a processing error that most likely occurs because the DEMs were created from data that had already been projected, while the LAS were created from data in a geographic coordinate system, and then received a projection. The DEMs and LAS should match in data content and extent. Dewberry has marked the locations of most of these edge rounding issues, however it is a systematic issue which requires a processing correction for all tiles.

30 Figure 28 LAS tile u313341_1_a_la shown as an ESRI masspoint in green. Overlaid is the DEM for the tile. DEMs on the edge of the project have rounded corners in comparison to the LAS. The DEMs were created from projected data, while the LAS existed in a geographic coordinate system before being projected Missing Pixels Four (4) calls were made for DEMs with missing pixels. Missing pixels in DEMs are single or clusters of pixels which contain no data. The data does exist in the LiDAR. This is a processing error which needs to be corrected. Figure 29 A large area of missing pixels in DEM tile u319335_3_b.

31 3.1.6 Misclassification in DEM One instance was found in which the classification of the DEM does not match the classification of the second delivery LAS tile. DEMs should always be created after modifications to the LiDAR and breaklines are complete. DEMs should match the bare earth LiDAR completely. In this case, the culvert is correctly classified as ground in the LiDAR. In the bare earth DEM, however, the culvert is removed along with legitimate ground on either side of the culvert. The DEM needs to be updated. As discussed in the breakline section of this document, the breakline should be split at the culvert. Hydro flattening must be ensured for the water bodies once they are separated. Figure 30 LAS tile u319352_3_b_la. LiDAR points are shown colored by classification. Pink points are ground, yellow points are unclassified, blue points are water and red points are buildings. There are no errors in the LAS tile. The culvert which separates the river from the pond structure is correctly classified as ground.

32 Figure 31 DEM tile u319352_3_b. The culvert shown above as well as portions of the ground on either side of it are missing from the DEM. The DEM should include all LiDAR ground points. The breaklines should be split around the culvert Divots in DEM Two divots were found in DEM tile u319351_1_b. These divots cannot be seen in the LAS and might be related to a processing issue. The divots are over 100 meters deep and must be corrected. Figure 32 Divot found in DEM of tile u319351_1_c. The divot appears only in the DEM of the tile, not the LIDAR. The DEM should be reprocessed.

33 3.2 Hydro Enforcement Review For hydro enforced breaklines and DEMs, water must be at or below the elevation of the surrounding terrain. As detailed in the breakline section of this report, a quantitative vertical variance calculation was performed using a terrain created from bare earth LiDAR points and the elevations of the three dimensional breaklines. A difference value was calculated for each vertex. Vertices with positive differences and vertices with notable negative differences were reviewed using the hydro enforced DEMs. Several cases of floating water and one case of digging water were detected Floating Water Floating water is not acceptable in hydro enforced datasets. Two hundred and seventy seven (277) floating water calls were made during the Sabine/Shelby DEM review. All cases of floating water should be addressed. It is expected that adjusting the breaklines for capture errors will considerably lessen the amount of floating water significantly. Figure 33 DEM tile u319301_4_c. A portion of a drainage water body which is floating by almost half a meter.

34 Figure 34 DEM tile u309312_1_d. A water body which floats in several areas. The entire water body should be lowered such that no vertices float Digging Water One (1) digging water body was found during the visual DEM review. The water body digs by almost 40 meters and must be corrected. This may be a DEM specific issue, since the vertices themselves did not signify any digging problems when compared to a terrain made from the LiDAR. Figure 35 DEM tile u319424_2_d. A water body digs by approximately 40 m.

35 3.2.3 Water Artifacts Water artifacts are any areas of water which are not flat or monotonically decreasing. These should not be present in hydro flattened water bodies. Sixteen (16) water artifacts were called in the Sabine/Shelby DEMs. All should be corrected. Figure 36 DEM tile u329463_4_c. Two water artifacts are seen in the profile of this stream. 4 Intensity Images Intensity data for the full project area were delivered. The intensities are 1 m pixel size as directed, however they are tiled similar to the LiDAR and DEMs based on USGS 1/16 th quadrangles, though with a slight overlap compared to the LiDAR tiling. The scope of work specifies Intensity images should use 1/4 th USGS quadrangles, (3.75 minute by 3.75 minute tiles) rather than 1/16 th quadrangles. 5 Metadata Metadata per tile was delivered for the LAS, DEMs and Intensities. Project level metadata was delivered for the breaklines. The metadata are sufficient with some comments; 1) the references to using classes 3, 4 and 5 for low, medium and high vegetation should be removed because they do not apply to this task order and are not used for all tiles. 2) The breaklines metadata file has a space in its file name that should be removed. 3) Errors were returned using ESRI s FGDC compliant metadata validation tool. The errors as returned by the tool are listed below. LiDAR: 7 errors: 1 misplaced, 5 missing, 1 bad value Error (line 107): Lineage is not permitted in Metadata Error (line 94): Process Date is required in Process Step Error (line 107): Fees is required in Standard Order Process Error (line 107): Digital Transfer Option is required in Digital Form Error (line 107): Format Name is required in Digital Transfer Information Error (line 107): improper value for Transfer Size Error (line 107): Process Step is required in Lineage

36 Breaklines: No errors DEMs: 8 errors: 1 misplaced, 1 too many, 4 missing, 2 bad value Error (line 109): Lineage is not permitted in Metadata Error (line 66): Time Period Information permits only one of Single Date/Time or Multiple Dates/Times or Range of Dates/Times Error (line 66): improper value for Calendar Date Error (line 109): Fees is required in Standard Order Process Error (line 109): Digital Transfer Option is required in Digital Form Error (line 109): Format Name is required in Digital Transfer Information Error (line 109): improper value for Transfer Size Error (line 109): Process Step is required in Lineage Intensity Images: 8 errors: 1 misplaced, 6 missing, 1 bad value Error (line 100): Lineage is not permitted in Metadata Error (line 96): Altitude Resolution is required in Altitude System Definition Error (line 96): Altitude Encoding Method is required in Altitude System Definition Error (line 100): Fees is required in Standard Order Process Error (line 100): Digital Transfer Option is required in Digital Form Error (line 100): Format Name is required in Digital Transfer Information Error (line 100): improper value for Transfer Size Error (line 100): Process Step is required in Lineage 6 GDB Dewberry will provide to TWDB a GDB and shapefiles that contain all the LiDAR, breakline, and DEM calls. Each deliverable will contain a separate feature class detailing the call, additional comments if needed, and for second delivery data, whether the call was fixed or not fixed. In this delivery, there is one additional polygon feature class for the area of the breaklines containing insufficient vertices and one polygon feature class identifying the flight line ridge. 7 Recommendation Summary The following represents a summary of Dewberry s recommendations. These recommendations can be found throughout the various sections of this report but are summarized here for convenience. LiDAR Calls Correct the tile with a high noise point classified to ground Correct the header record issues including projection information, GPS time records and scan angle records. Reclassify points in extraneous classes Ensure the LAS are properly tiles to the USGS 1/16 th quadrangle system Correct all new or remaining edit calls including the flight line ridge, divots, artifacts, and misclassifications. Update ground and water classification after all breakline edits are complete TWDB should evaluate the issue of divots that cannot be detected by standard procedures. Breakline Calls Project the breaklines according to project specifications Separate the breaklines into three shapefiles Remove the islands breaklines from the water feature breaklines

37 Address all breakline capture calls made by Dewberry including missing features, breaklines that need to be removed and ground captured as water Correct the one breakline crossing breakline boundary error Address all monotonicity errors TWDB should evaluate the issue of loss of detail due to an insufficient number of vertices that affects about half the project DEM Calls The two DEMs that do not display should be processed and reviewed Correct for the edge tinning artifacts and assure the DEMs are properly tiled to the 1/16 th USGS 7.5 minute quadrangle tiling scheme Ensure the DEM extents match the LAS extents and do not have rounded corners After all breakline digitization changes are complete, address the areas of floating water identified by Dewberry. Correct all other calls identified by Dewberry; a digging water body, water artifacts, missing pixels, DEM divots, and DEM misclassification. Once all breakline and LAS calls are addressed, the DEMs should be reprocessed Intensities Should be retiled according to 1/4 th USGS 7.5 minute quadrangle tiling scheme Metadata The LAS, DEM, and Intensity made metadata should be made FGDC compliant The references to classes 3, 4, and 5 should be removed The breaklines metadata file should be renamed without a space

38 Memorandum To: Jeff Poplin, Andrew Peters From: Sarah Sleyman Date: Subject: Remaining Errors in Sabine/Shelby Third Delivery This review is for the third delivery of the LiDAR, breaklines and DEMs for Sabine and Shelby Counties, Texas. In March 2012, a full review was done on the second delivery data which included second delivery LiDAR and breaklines and a first full delivery of the DEMs. The majority of errors identified in that review have been corrected for the third delivery, however, further corrections will be needed to ensure the data meets project specifications. A summary of issues identified during the second review and the current status of the issue is listed below: LiDAR A high ground point in tile u319341_1_c has been corrected. Projection information in the LAS header information has been corrected with the exception of one tile. As identified by the data provider, the GPS timestamp and sensor scan angle irregularities in the LAS header information have not been addressed. See below for more information. Many points in extraneous classes have been corrected, however points still exist in classes 11, 17 and 21. See below for more information. The LAS tiling scheme adheres to that provided by TWDB. Dewberry feels there is a slight discrepancy between the provided tiling scheme and the USGS 1/16 th quadrangle tiling system, however this is not an error associated with the data. All edit calls for misclassifications, artifacts and divots have been corrected. Two data voids which appeared in the second delivery have been corrected. Edit calls identifying a flight line ridge have not been fully corrected. Please see the examples below for more information. Breaklines Missing breakline projection information has been corrected; the breaklines are now projected according to project specifications. As recommended, the breaklines have been separated into separate shape files representing Drainage, Islands and Ponds. Breakline overlap issues have been corrected. All islands are now removed from pond or drainage breaklines. Breakline capture quality issues including capturing areas of ground as water and not capturing river banks have been corrected. One identified crossing feature was corrected in the breaklines. Monotonicity errors called in the second delivery breaklines were corrected, however a small number of new monotonicity errors were detected. Dewberry originally noted that some areas of breaklines were captured with fewer vertices and therefore less detail than other sections. TWBD has evaluated the issue and determined that the level of detail in the breaklines is sufficient for their needs. 1

39 Memorandum DEMs Two DEMs that did not display correctly in the second delivery have been corrected. Edge tinning artifacts are no longer present in the DEMs (except for one case which has been called as a new error). Instead, DEM edges contain additional buffered data that is not contained in the LiDAR. In general this solution is acceptable, though in some cases the additional data does not exactly mach the main data set. Please see the DEM section below for more information. The DEMs no longer display rounded edges. DEM extents are now suitable for the project. The majority of floating water detected in the second delivery have been corrected however some floating water remains and, though not severe, should be addressed. New water artifacts have appeared in the redelivered DEMs and will require corrections. All water artifacts originally identified have been corrected. All other DEM quality calls including digging water and missing pixels have been corrected. Intensities Are tiled according to the USGS 1/16 th quadrangle system with an approximately 30 m buffer. Metadata As identified by the data provider one lineage error and one process step error which are not FGDC compliant have not been addressed. As recommended, the references to classes 3, 4, and 5 have been removed from the metadata files. The breaklines metadata files are now properly named. Vertical Accuracy Because the LiDAR has received two sets of edits vertical accuracy calculations were rerun for this delivery. The vertical accuracy passes all project specifications. Table 1 outlines the calculated RMSEz and associated statistics while Table 2 outlines vertical accuracy and the statistics of the associated errors as computed by the different methods. 100 % of Totals RMSE Z (m) Spec=0.125 m 1 Mean (m) Median (m) Skew Std Dev (m) # of Points Min (m) Max (m) Consolidated Open Terrain High Grass Forest Urban Table 1: The table shows the calculated RMSEz values in meters as well as associated statistics of the errors for Sabine/Shelby, Texas. 1 In open terrain. 2

40 Memorandum Land Cover Category # of Points FVA Fundamental Vertical Accuracy (RMSE Z x ) Spec=0.245m CVA Consolidated Vertical Accuracy (95th Percentile) Spec=0.363m SVA Supplemental Vertical Accuracy (95th Percentile) Spec=0.363m Consolidated Open Terrain High Grass Forest Urban Table 2: The table shows the calculated Accuracy z of the FVA in meters using FEMA/NSSDA guidelines (RMSEz x ) and the Accuracy z of the CVA in meters using NDEP/ASPRS guidelines (95 th percentile) for Sabine/Shelby, Texas. The data delivered for Sabine/Shelby, TX has an RMSE Z in open terrain of m which meets the v13 USGS specifications. The fundamental vertical accuracy is m which meets the project specification of m. In addition, TWDB has an additional requirement that the points in Forest need to meet an RMSE of 0.25 cm which they do at 0.16 m. Dewberry identifies no issues with the vertical accuracy as delivered for Sabine/Shelby Counties, TX. Remaining Issues Issues that remain and need corrections include some LAS header information inconstancies, one flight line ridge, some DEM edge inconsistencies, one DEM edge artifact, one area of water that is not flat between DEM tiles, a small number of water artifacts, a small number of floating water issues, and a small number of monotonicity errors. Examples of all remaining errors are provided below: LAS Header Information 1. Tiles u319350_2_d_la.las, u319351_2_b_la.las, u319351_2_d_la.las, and u319351_3_a_la.las are in LAS version 1.0. For constancy, these tiles should be formatted in LAS version Tile u309303_3_c_la is missing all projection information in its header information and has additional inconsistencies compared to all other tiles including its generating software, variable length record and offset to data length. 3. Five tiles which contain points in extraneous classes remain in the third delivery. Project specifications state that all points should be classified as either class 1, 2, 6, 7, 9 or 13. Tile Additional Classes u319360_2_c_la 21, 17 u319358_4_a_la 21 u319351_2_a_la 21 u319351_1_b_la 21 u319351_1_a_la 21 3

41 Memorandum U319317_1_b_la 11, The system_id field was blank for all tiles in the previous delivery but is now populated for 11 of the 433 tiles creating an inconsistency. 5. As stated by the data provider with the third delivery, corrections have not been made to the 242 tiles which show incorrect minimum and maximum GPS timestamps. 6. As stated by the data provider with the third delivery, corrections have not been made to the anomalous minimum and maximum scan angle records for several tiles. LiDAR 1. A cm flight line ridge called in the previous delivery has not been sufficiently corrected. This ridge is caused by one flight line which seems to have been flown at a different time than the surrounding lines. The ridge was partially corrected through classification, but a more universal fix is needed. Figure 1 u309303_1_d. This flight line ridge ranges from 20 to 50 cm and was not fully corrected in the third delivery LAS. 4

42 Memorandum Figure 2 LAS profile of tile u319359_1_d_la colored by source ID (top) and classification (middle). In the top image, points in the flight line colored purple are approximately 35 cm lower than points in the flight lines colored blue and green. The second profile shows how ground points have been classified to accommodate for the offset. A more systematic fix is recommended. DEMs 1. The DEMs for the project have a projected coordinate system (UTM Zone 15 N) and contain overlap. In the previous DEM delivery, many edge DEM tiles displayed tinned edge artifacts. To correct for this and to maintain square DEMs, DEMs located on the edge of the project boundary now contain small strips of additional data that are not present in the LAS. Often, the additional data will have received slightly different processing than the main data. This can result in a ridge where the data join. These ridges are sporadic and in general measure fewer than 10 cm. Because the large majority of the edge ridges are under specification and because they do not affect the quality of the data in the main area of interest, Dewberry feels the correction is acceptable. 5

43 Memorandum Figure 3 DEM tile u309320_1_a shows an example of edge ridges seen throughout the Sabine/Shelby DEMs. The ridges are formed where additional data has been added to the DEMs to ensure rectangular tiles. The majority of the ridges are less that 10 cm and do not affect the quality of the main data. This ridge is around the 10 cm range but varies within the tile. Figure 4 DEM tile u309320_1_a with LAS tile u309320_1_a_la overlaid as points. Because DEMs are required to be rectangular while LAS are not, the DEMs include additional buffer data that is not included in the LAS. 2. One tinned edge artifact remains in the DEMs. This should be corrected using additional data in the same way as other DEM edge tiles were addressed. 6

44 Memorandum Figure 5 DEM tile u309312_3_d contains a tinning artifact along one edge. This should be corrected using additional buffer data. 3. One area remains where the water is not flattened between tiles. This error was present in the previous DEM delivery but was not called because the tiles contained large divots which distorted the color ramp of the DEMs and hid the error. (The divots have been corrected.) Figure 6 DEM tile u319351_1_d (bottom right). Water in this tile is 25 cm higher than in the two adjacent tiles. 4. Five water artifacts remain in the DEMs. These were not present in the previous DEM delivery. 7

45 Memorandum Figure 7 DEM tile u319360_2_a. A water artifact has appeared the DEMs that was not present in the previous delivery. This artifact measures approximately 30 cm in height. 5. The breaklines received extensive edits for the third delivery. Because of this, vertical variance checks were performed again on the updated breaklines. Some floating water remains; it is not severe but should be corrected. Figure 8 DEM tile u319352_4_a. Water in this area floats by 5 to 10 cm. Floating water is not acceptable in hydro flattened DEMs. Breaklines 1. Because they have received extensive edits between deliveries, full automated and visual checks were run to ensure quality and monotonicity of the third 8

46 Memorandum delivery breaklines. A small amount of monotonicity errors requiring corrections have appeared in this delivery. Figure 9 DEM tile u309304_1_b showing a monotonicity error in a hydro flattened stream. Streams should be flat or monotonically decreasing. 2. As a final step, the breaklines could be clipped to the project boundary unless the client prefers keeping the buffer. Figure 10 The breaklines cover the Sabine/Shelby project area with an approximately 350 meter buffer. GDB The GBD provided with the previous review has been edited to indicate whether every edit call made for LiDAR, Breaklines, and DEMs has been corrected or not corrected. 9

47 Memorandum New errors have been added to the GDB and are labeled New Call. All edits calls with either New Call or Not Fixed in their latest Review column need further corrections from the data provider. 10

48 Memorandum To: Felicia Retiz From: Sarah Sleyman Date: Subject: Hydro-flattening review of DEMs for Sabine/Shelby fourth delivery I have completed a targeted review of the fourth delivery data DEMs for Sabine and Shelby Counties, TX. Results can be divided into two areas of concern: water surface anomalies, and floating water. For the hydro-flattened surface anomalies, three issues remain which should receive corrections. Any other surface anomalies will not significantly impact the DEMs. In regards to floating water, some floating water calls made during the third review of the data were not corrected aggressively enough. Occasionally, floating water has appeared as a result of correcting monotonicity errors. Ten remaining areas of floating water should receive further corrections. All corrections should be done carefully to avoid creating new errors. Please note that no remaining surface anomaly or floating water errors intersect with the priority tiles you indicated by in May of Water Surface Anomalies: I recognize your concerns in regards to the hydro surface anomalies, but after reviewing select DEM tiles including the three indicated in your , as well as screen shots you shared with GeoEye and Dewberry on June 6 th 2012, I feel that while the hydro-flattening for rivers in this project is not as clean as it could be, the majority of water surface anomalies we are seeing are on par with industry standard expectations and will not significantly affect the usefulness of the data. Global Mapper is our go-to tool for DEM review at Dewberry, however much of its usefulness comes the fact that it is very sensitive in the way it displays surface changes. Because of this, anomalies both in the ground and in the hydro-flattened water tend to look exaggerated. Hydro-flattening DEMs involves using (primarily) automatic tools to assign appropriate elevations to all data existing within the project breaklines. These elevations are based off of the LiDAR elevations at the breakline itself, which are inherently variable. It is in this stage that errors are introduced into the DEM hydro features, and further automatic or manually methods must be used to fix these errors. The Sabine/Shelby documentation states that hydro-flattening should refer to DRAFT Base LiDAR Specification Version 13 which requires flat and level bank-to-bank (perpendicular to the apparent flow centerline) gradient to follow the immediately surrounding terrain for inland streams and rivers. However, while it is not explicitly stated in Version 13, a small error tolerance is inherent in hydroflattened rivers and streams. This is a nearly unavoidable result of compromising between staying close 1

49 Memorandum to the changing elevations of the LiDAR at the stream banks while flattening and decreasing the stream. The tolerance is quite small; generally we would suggest corrections to water surface errors that exceed just 1 or 2 cm. Also considered is how the error appears in the DEM. Typically, it has become industry standard to ignore occasional hydro-flattened river surface errors of less than 1 cm. For this delivery, in addition to running automated checks of the full breaklines, I visually reviewed all DEMs that had been called as having errors in the third delivery Dewberry review as well as/in particular the three tiles you mentioned in your (u309304_1_b.dem, u319352_4_a.dem and u329464_3_c.dem). Whenever corrections are made to DEMs, there is a possibility of introducing new errors. (This is the main reason we continue to find errors after several reviews of this data.) Keeping this in mind while doing my review, I called three water surface errors that need to be corrected further, one of which was pictured in your screenshots. Surface errors other than these three are consistent with the general error tolerance of hydro-flattened DEMs, and, because of this and the possibility of creating new errors, are not being recommended for further correction. Pictured below are the three errors that should be corrected. When correcting these errors, hydro elevations should always be lowered and never raised. This will ensure no new floating water errors are created. Figure 1 - DEM tile u319352_4_a. Further hydro-flattening corrections are needed around this island. Breakline e values surrounding the island are approximately 10 cm higher than the breakline z values of the surrounding banks. The breaklines elevations surrounding the island should be adjusted; digging water around the island is acceptable to maintain flatness. 2

50 Memorandum Figure 2 - DEM tile u309343_3_b. A water artifact of several centimeters has not been corrected. Figure 3 - DEM tile u319352_4_c. While not a major issue, this monotonicity error of approximately 3 cm is large enough to warrant corrections. Floating Water: Of greater concern than the water surface anomalies is remaining floating water in the DEM data set. Under USGS Version 13 Specifications, no portions of a water body should be floating. This becomes especially important for hydrologic and hydraulic modeling. As with water surface anomalies, though it is not expressly stated, a small error tolerance is inherent in DEMs where floating water is concerned, 3

51 Memorandum but every effort should be made to keep this very small. Along rocky cliffs or stream banks, some isolated floating vertices may appear. These are generally not considered an error so long as they are small (not exceeding a few centimeters) and so long as the floating does not become a trend in the area. For the Sabine and Shelby DEMs, several floating water calls were made in the previous deliveries. For this delivery, there are some cases where the floating has still not been corrected aggressively enough, or where floating water has occurred as a result of correcting other errors. During this review, I located ten areas of floating water remaining in the DEMs which are substantial enough to be recommended for further corrections. One of the ten areas is the result of a previous monotonicity correction and is approximately 30 cm; all others are smaller errors. When correcting floating water, it is acceptable to lower entire sections of the stream (so long as monotonicity is maintained) even if this causes digging water. Digging is a necessary and unavoidable consequence of hydro-flattening, and extended moderate digging is much preferred to intermittent floating. For most of the problem areas, I have placed a marker at the beginning and end of the floating water. To reiterate not all vertices within these marked areas float, and the floating is generally minor, but in order to get the best quality product, I do feel it worthwhile to correct them. Examples of remaining floating water are provided below. Figure 4 - In correcting monotonicity errors in this river, a vertex has been made to float by about 30 cm. The floating must be corrected while maintaining monotonicity and creating as flat a surface as possible from bank to bank. 4

52 Memorandum Figure 5 - DEM tile u319352_4_a. Enough floating vertices remain in this area to justify lowering the water further. Figure 6 - DEM tile u319360_4_c. Enough floating vertices remain in this area to justify lowering the water further. 5