Significant Wave Height products :

Transcription

1 Significant Wave Height products : dataset-wav-alti-l3-nrt-global-j3 dataset-wav-alti-l3-nrt-global-s3a Contributors: N. Taburet, R. Husson Approval date by the CMEMS product quality coordination team: 19/09/2017

2 CHANGE RECORD When the quality of the products changes, the QuID is updated and a row is added to this table. The third column specifies which sections or sub-sections have been updated. The fourth column should mention the version of the product to which the change applies. Issue Date Description of Change Author Validated By 1.0 April 2017 All Creation of the document Nicolas Taburet R. Husson 28/06/2017 Update the metrics definition and illustration R. Husson R. Husson Page 2/ 31

3 TABLE OF CONTENTS I Executive summary... 4 I.1 Products covered by this document... 4 I.2 Summary of the results... 4 II Production system description FOR ALtimeTER DATA... 5 II.1 Production center name... 5 II.2 Operational system name... 5 II.3 ABC of the altimeter-derived SWH measurements... 5 II.4 Production centre description for the version covered by this document... 7 II.4.1 Introduction... 7 II.4.2 Altimeter Input data description... 8 II.4.3 Acquisition processing... 8 II.4.4 Editing... 9 II.4.5 SWH calibration II.4.6 Along-track (L3) Product generation II.4.7 L3 Quality control III Validation framework IV Validation results IV.1 Significant Wave Height IV. Data availability over the calibration period IV.1.2 Data editing over the calibration period V System s Noticeable events, outages or changes VI Quality changes since previous version VII References Page 3/ 31

4 I EXECUTIVE SUMMARY I.1 Products covered by this document This document describes the quality of the operational (NRT) Significant wave height products listed here after: product Area satellites Spatial resolution Temporal resolution Global ocean Jason-3; Sentinel-3A Along-track ~7km (full 1Hz resolution) 10 days to 27 days (variable with satellite cycle length) ; products are stored in one file per pass. I.2 Summary of the results The quality of the SWH L3 measurements from Sentinel-3A and Jason-3 has been estimated using intercalibrated SWH measurements with crossovers. Jason-3, a conventional altimeter, is used as a referenced to correct Sentinel-3A SWH L3 measurements, after editing, for both the Synthetic Aperture Radar (SAR) and Pseudo-Low Resolution Mode (PLRM) modes. Sentinel-3A crossover points with Jason-3 were computed at global scale on a 140-day period (November 23th 2016 to April 9th 2017). After applying the editing criteria for selecting only the best quality data, 36.7%, 18.5% and 18.9% data are rejected for, respectively, J-3, S3-A SAR mode, S3-A PLRM mode data. Jason-3 is used as the reference with respect to Sentinel-3A, as it is a conventional altimeter mission, and expected to show robust results for SWH measurements. Sentinel-3 data in SAR mode and PLRM mode are both inter-calibrated with respect to this reference. With respect to Jason-3, Sentinel-3A SAR data shows a mean bias of 6.34cm and a standard deviation of 22.74cm for all crossovers. With respect to Jason-3, Sentinel-3A PLRM data shows a mean bias of 3.56cm and a standard deviation of 27.06cm for all crossovers. Page 4/ 31

5 II PRODUCTION SYSTEM DESCRIPTION FOR ALTIMETER DATA II.1 Production center name SL-CLS-TOULOUSE-FR II.2 Operational system name The operational chain is given a generic name: the L3 alti wave chain. II.3 ABC of the altimeter-derived SWH measurements The altimeter sends a spherical radar signal in the direction of the nadir. This signal is reflected by the sea surface and goes back to the satellite. The analysis of the returned signal allows the calculation of the time needed by the signal to go and come back i.e. the distance satellite-sea surface. The sea state surface elevation distribution impacts the speed at which the return signal is fully returned to the satellite. Hence, the Significant Wave Height (SWH) over ocean surfaces is determined from the slope of the front in the radar altimeter wave form. The higher the waves, the more the returned signal is spread in time. Hence, a long delay between the first returns and a full signal return will result in a long shadow in the wave form, which then indicates a high sea state (Figure 1). The term Significant Wave Height (also sometimes denoted H s ) refers to the wave height of the larger one third of the waves (also sometimes denoted H 1/3 ). Page 5/ 31

6 Figure 1: Formation of an echo over a sea surface with waves for conventional altimetry Figure 2: the altimeter waveform Page 6/ 31

7 II.4 Production centre description for the version covered by this document II.4.1 Introduction The system s primary objective is to provide operational products of calibrated significant wave height (Hs) data for the Jason-3 and Sentinel-3A missions. The processing sequence can be divided into 4 main steps, illustrated in Figure 3: Acquisition Data editing Calibration Product generation L2-ACQUISITION CRON Start L3 production DataUpdate RPC Client L3-PRODUCTION DAD SAD PRE-PROCESSING (data acquisition) DATA UPDATE Internal database EDITING (valid mesures selection) L2 Files CALIBRATION FILES GENERATION (NetCDF ) PRODUCT QUALITY MONITORING L3 Product Quality Report L3 NRT (near real time) Figure 3 L3 Alti wave production component Page 7/ 31

8 II.4.2 Altimeter Input data description The altimeter measurements used in the system consist in Near Real Time products (OGDR or NRT) Level2 products from the different missions. Their source and availability delay are summarised in Table 1 whereas altimeter missions characteristics are presented into Table 2. Altimeter mission Type of product Source Availability delay Sentinel-3A NRT ESA/EUMETSAT ~3h Jason-3 OGDR EUMETSAT/NOAA ~3h Table 1: Source and delay of availability of the different altimeter data Altimeter mission Cycle duration (days) Latitude range ( N) Number of tracks in the cycle Inter-track distance at equator (km) Sentinel-3A 27 ± ~100 Yes Sunsynchronous Technology SAR + PLRM Jason-3 10 ± ~315 No LRM input data availability Start- End dates 2016/12/13 (cycle 12) Ongoing 2016/02/17 (cycle 1) Ongoing II.4.3 Acquisition processing Table 2: Altimeter missions characteristics and L2 products availability period The acquisition processing has two main functions: Acquisition and Synchronization of dataflow illustrated in Figure 4. File acquisition The purpose of the acquisition is to acquire new L2 files and new ancillary data (AUX files) needed to compute the products (Orbit file, external corrections, etc.) for each data source. Each L2 file acquired can be updated with its availability date read on the source server. This ensures using the most recent inputs files and avoiding unnecessary updates. Data synchronization The synchronization function is synchronizing L2 data with all ancillary data (AUX files) needed to process L3 data. Once the L2 data and all the associated ancillary data are available, they can be used for L3 production. Page 8/ 31

9 L2 NRT (near real time) AUX (ancillary data) L2-ACQUISITION ACQUISITION DATA SYNCHRONIZATION (ADEA) notification Files L3-PRODUCTION II.4.4 Editing II Editing criteria Figure 4 L2 Alti wave acquisition processing Quality Control on the input L2 data is a critical process applied to guarantee that the system uses only the most reliable altimeter data. The system is supplied with L2 products that contain data directly derived from the altimeter measurements (e.g. range, sigma0 ) as well as geophysical data (e.g. dry tropospheric correction, significant wave height ) and flags (e.g. surface type, ice presence ). These values are provided at high (20Hz for Jason-3) and low (1Hz) frequency. Only the 1Hz data are used in the system. Data are selected as valid or invalid using a combination of various criteria such as quality flags or parameter thresholds. Details of threshold editing are presented in Table 3. These criteria are adapted from the ones used for the Sea Level Anomaly (e.g. Aviso/SALP 2016). Criteria related to retracking derived values were selected while geophysical parameters were not (e.g. tropospheric corrections ) since they do not intervene in the SWH estimation. For Sentinel-3A the criteria on the off nadir angle is not activated since this value is not derived from the retracking in SAR mode and therefore its value does not provide information about data quality. An estimate of the percentage of rejected measurements is also provided in Table 4. These values were obtained by applying the editing described in Table 3 on about 150 days of data. The rejection level due to the surface type flag on S3-A data is very low, this is explained by the use of the Ocean Sentinel-3A products in our editing and calibration tests processes. The overlap between the land and ocean products is of the order of 300km and therefore explains the 2% rejection level with the surface type flag. Thanks to the high quality of current missions, the threshold criteria reject a small percentage of altimeter measurements. Page 9/ 31

10 Parameter Method J3 S3-A SAR S3-A PLRM Ice Flag Flag value Valid value : 0 or 5 Valid value : 0 Valid value : 0 Surface type Flag Flag value Valid value : 0 or 1 Valid value : 0 Valid value : 0 Swh [m] Sigma0 [db] Square off nadir angle threshold threshold threshold Wind speed [m/s] threshold Orbit - range [m] Sigma0 standard deviation [db] Range standard deviation [m] threshold threshold threshold Min : 0 max : 30 Min : 9.38 max : Min : -0.2 max : 0.64 Min : 0 max : 30 Min : -130 max : 100 Min : 0 max : if distance to shoreline < 50km : 2.5 else : 1 Min : 0 max : *swh+0.2 Min : 0 max : 30 Min : 5 max : 28 Min : 0 max : 30 Min : -130 max : 100 Min : 0 max : 0.7 Min : 0 max : 0.02*swh+0.12 Min : 0 max : 30 Min : 5 max : 28 Min : 0 max : 30 Min : -130 max : 100 Min : 0 max : 0.7 swh_numval_ku threshold Min: 10 Min: 18 Min: 18 swh_rms_ku threshold Min: 0 Min: 0 Min: 0 Table 3: Editing criteria Min : 0 max : 0.015*swh+0.18 Page 10/ 31

11 Parameters J3 S3-A SAR S3-A PLRM Ice Flag Surface type Flag (see text for explanation) 2.20 (see text for explanation) Combined Flags Swh Sigma Square off nadir angle 0.56 N/A N/A Wind speed Orbit - range Sigma0 standard deviation Range standard deviation Combined thresholds All criteria Table 4: Percentage of rejected measurements estimated over J-3 and S3-A data acquired from November 23th 2016 to April 9th 2017 II SWH editing quality from cross-overs Figure 5 presents the dispersion of the S3-A SAR J3 SWH differences at 3h crossover points as a function of the 10cm width bins of S3-A SWH. Blue and red curves respectively represent the editing presented in this section (hereafter wave editing) and the editing used for sea level estimation. Performances of the wave editing are similar to the full sea level version but as shown in the bottom panel allows having about 6% more points due to the relaxed constrains on geophysical parameters. Figure 6 presents the same analysis between the SAR and PLRM Sentinel-3A points, a much larger dataset since they are all co-located. The gain is of the order of 1%. Page 11/ 31

12 Figure 5: Top: Dispersion of the S3-A SAR J3 SWH difference at crossover points per 10cm bins. Bottom: number of crossover valid points Page 12/ 31

13 Figure 6: Dispersion of the S3-A SAR S3-A PLRM SWH difference points per 10cm bins. Bottom : number of valid points II SWH editing quality from SWH dispersion Queffeulou [2016] represents the 1Hz measurement in the SWH / SWH rms plane to assess their quality. They proposed a criterion based on a maximum SWH rms as a function of SWH to eliminate potentially erroneous data. Representing the Jason-3 and Sentinel-3A data before and after application of the editing in this SWH / SWH rms plane shows that the editing significantly decreases the quantity of data in the high SWH rms area (Figure 7). As explained in Queffeulou [2016] the area for SWH < 1.5m presents a non-linear behaviour of the rms on all altimeters and may be due to waveform processing. Page 13/ 31

14 a) b) c) d) e) f) Figure 7: Top Left (a) : Jason -3 data in the SWH / SWH rms plane without editing. Right (b): same after editing Middle Left (c): Sentinel -3A SAR data in the SWH / SWH rms plane without editing. Right (d): same after editing Bottom Left (e): Sentinel -3A PLRM data in the SWH / SWH rms plane without editing. Right (f): same after editing Page 14/ 31

15 II.4.5 SWH calibration Calibration is divided into two steps as detailed in Figure. The first one consists in homogenising the data from different altimeters. Hs measurements of every single mission are calibrated on those of a reference mission (Jason-3). The second step consists in the application of a correction between the reference mission and in situ measurements provided by buoys. Mission 1 Mission 2 Mission N Calibration on reference mission Reference mission Calibration on in situ data InSitu Measurements Figure 8 : Calibration process II Cross-calibration Cross-calibration consists in determining the relation between the Hs provided by 2 different missions. This relation is determined on a representative number of measurements and then used in the operational system to homogenise the missions with respect to the reference one. Such a relation is expected to remain valid as long as instrumental drifts are not detected or ground segment evolutions does not affect the L2 products in input of the operational system. Should one of these evolve another cross-calibration relation determination should be performed and implemented into the operational system. Depending on the orbit of the mission to be calibrated with respect to the orbit of the reference mission 2 different methods can be considered. The first one is available during the validation phase, if it exists, between 2 missions: both satellites are on the same orbit separated by a few minutes. A very large number of spatially collocated measurements are therefore available for cross calibration. The second method is employed when the two missions are on different orbits or no validation phase is available. Crossover points between both orbits are the determined. For Hs measurements calibration only crossover points with a time difference lower than 3 hours are considered. This time value ensures that both missions observe a scene that did not significantly evolved (when a longer dataset archive is available, this time difference can be lowered to 1 hour). The 1Hz along track data for each mission is then interpolated at the selected crossover points. The interpolation technique consists in spline approximation and accounts for the average noise associated with Hs measurements, such values were taken to be 12 and 9 cm for Jason-3 and Sentinel-3A respectively. As described in the Sentinel-3 User Handbook, Hs measurement requirements is 2% for the S3 NRT products. Page 15/ 31

16 After Hs values from the mission to be calibrated and the reference mission have been collocated using one of the two previous methods, Hs value differences are computed. The results are expressed as a function of the Hs in order to provide a bias correction depending on the significant wave height. The selected reference mission is Jason-3. II.4.5. Sentinel-3A cross-calibration with Jason-3: Sentinel-3A crossover points with Jason-3 were computed on a 140-day period (November 23th 2016 to April 9th 2017). The starting date corresponds to the beginning of the production of S3-A product with the Samosa 2.3 ocean retracking that is used to determine the Hs from the waveform. Figure 8 presents the spatial distribution of the valid crossover points after editing. The number of points is more important at high latitudes in the south hemisphere, allowing sampling higher waves. Figure 8: Spatial distribution of Sentinel-3A and Jason-3 cross-over points. Only valid points after editing are displayed. Top: histogram of the selected points. Right: Number of points and mean Hs valid values as a function of latitude. The representativeness of the crossover points with respect to the ensemble of valid along-track points is assessed by comparing the two distributions (Figure 9). The distribution of the crossover points is skewed towards larger Hs values due to the higher density of crossover points at high latitudes where the mean Hs is higher than in the inter-tropical band. Despite this distribution differences, crossover points over the cross-calibration period sample all range of significant wave height values from 0.5 to 6m. Outside of this interval, the population in each bin of 10cm width is smaller than 10 points and the cross-calibration fit is likely to be less reliable. Page 16/ 31

17 Figure 9: Valid Jason-3 points distribution over the cross-calibration period S3-A SAR Hs values are grouped within 10cm width bins. The blue dots in Figure 10 represent the median of the difference between the S3-A SAR values and the Jason-3 ones inside each bin population. A second order polynomial fitting function is then adjusted, accounting for the error bars, to determine this bias function. Such a non-linear fit is performed to account for the higher order dependency of the bias with the significant wave, particularly visible on Figure 12 where S3-A PLRM and S3-A SAR modes SWH measurements are directly compared. A second order polynomial fitting function of S3-A SAR Hs was performed. As presented in Figure 10 and Figure 12 such an approximation is relevant. The top plot in Figure 10 presents two fitting functions, computed on the 0-6m range and the 0-12m range in orange and green respectively. Both polynomials are in good agreement over the 0-6m range but significantly differ from more than 10cm for higher Hs values. Residuals between the proposed fitting polynomial and data are presented in the bottom plot. As expected the fitting function over the 0-6m range presents a low bias and dispersion over this range (orange) but it is strongly biased (10cm) when accounting for the whole population (yellow). The fitting function computed over the 0-12m range has a 6cm mean bias and a large dispersion induced by the poorly sampled high values. When using 0-6m Hs values, the fit is unbiased and the dispersion is lower than the 9cm accuracy over the Hs values. Such a fit nevertheless presents large uncertainties for Hs values larger than 7m. Crossover points between S3-A and J3 only provide about 5000 measurements. The distribution tail for Hs values higher than 6m is under-sampled (red curve in Figure 9). Neither the computation of the SAR S3-A Hs bias with respect to J3 nor the extrapolation of the fitting function determined over the 6-12m range can be performed accurately. Nevertheless the PLRM S3-A Hs vs J3 Hs bias is expected to be linear as a function of the significant wave height, crossover points can therefore be used in order to calibrate the S3-A-J3 bias relationship on S3-A PLRM measurements (Figure 11). Although the dispersion remains important due to the poor statistics at large Hs values, the mean bias is of the order of +/-3cm.Both fits on the 0-6 or 0-12m range (orange and green curves respectively) are in good agreement and less affected for high waves than with a direct fit of the SAR over the Jason-3 values. Page 17/ 31

18 Using the simultaneously valid PLRM and SAR S3-A measurements over the same period (about 7 million points) the SAR vs PLRM bias fitting function can therefore be accurately computed over the whole 0-12m range (Figure 12). With very few data over 12m Hs these measurements are not used to determine the fitting function. The SAR vs PLRM bias is assumed to remain constant for higher Hs values. Combining the SAR vs PLRM and S3-A PLRM vs J3 bias corrections, a global fitting function allows to inter-calibrate S3-A SAR Hs on J3 Hs. Figure 13 shows that this 2 stage inter-calibration process (red curve) is in good agreement on the 0-6m range with the direct S3-A SAR vs J3 calibration using the crossover points (green curve). The direct method is nevertheless much more uncertain on the 6-12m Hs range due to a much lower number of measurements with such values. The uncertainties are driven by the stage using crossover points. The residuals bias is of the order of 3 cm for the 2 stage method and is lower than the 6-10cm bias found with the direct method. The 2 stage inter-calibration process is therefore implemented in our system to calibrate S3-A SAR on J3. Figure 10 : Top: Median of the difference between the S3-A SAR Hs value and the J3 value per 10cm bin. Error bars represent the standard deviation of the difference inside each bin. The orange and green curves represent different second order fitting polynomials. Bottom: Residuals between the median and the fits (see text for details). Page 18/ 31

19 Figure 11: Top: Median of the difference between the S3-A PLRM Hs value and the J3 value per 10cm bin. Error bars represent the standard deviation of the difference inside each bin. The orange and green curves represent linear fits over the 0-6 and 0-12m ranges respectively. Bottom: Residuals between the median and the fits. The mean bias is of the order of 3 cm. Figure 12: Top: Median of the difference between the S3-A SAR Hs value and the PLRM value per 10cm bin. Error bars represent the standard deviation of the difference inside each bin. The orange curve represents the second order fitting polynomial. Bottom: Residuals between the median and the fit. The mean over the 0-12 m range shows that the residuals are unbiased. The dispersion is of the order of 3cm. Page 19/ 31

20 Figure 13 : Top: Median of the difference between the S3-A SAR Hs value and the J3 values per 10cm bin. Error bars represent the standard deviation of the difference inside each bin. The red curve represents the combination of the second order fitting polynomial between the S3-A SAR and PLRM values as well as the linear fit between S3-A PLRM and J3 values. The green curve is the direct fitting function between the S3-A SAR and J3 values at crossover points. Bottom: Residuals between the median and the fit. The bias is of the order of 3cm. II Absolute calibration According to results from Queffeulou [2016], performances for JASON-3 are very similar to those given by JASON-2. The same linear correction can thus be applied to compensate for systematic errors. This correction is thus also applied to all other inter-calibrated missions. The linear correction is given below [Queffeulou and Croizé-Fillon 2017]: swh_cor = x swh Equation 1: Jason-2 linear correction for SWH Comparisons between JASON-3 and JASON-2 along-track 1 Hz collocated measurements during JASON- 3 commissioning (same track, 80s difference between the two altimeters), were performed to compare sea state sensed by the two altimeters at the same geographical location (Figure 14). Page 20/ 31

21 Figure 14: JASON-3 and JASON-2 1 Hz collocated SWH are in very good agreement (SWH RMS filtering applied). The regression line is close to the perfect one. The bias is less than 2mm and the rms is about 19 cm. The right plot shows a symmetrical distribution of the SWH which indicated similar precisions. Extracted from Queffeulou [2016]. II.4.6 Along-track (L3) Product generation The bias correction described on the previous section is applied on the Hs values for Sentinel-3A and Jason-3 data. One NetCDF file per pass is generated for each mission. As explained in section II.4.3, due to the successive treatments as soon as each elementary data are available, the generated L3 products contain the most recent and complete set of data. The L3 along-track products contain the fields described in Table 5. Standard name Long name NetCDF Type units time time (sec. since ) TAI (International Atomic Time) double seconds since :00:00.0 latitude latitude int 10-6 deg longitude longitude int 10-6 deg sea_surface_wave_significant_height II.4.7 L3 Quality control significant wave height on main altimeter frequency band Table 5: Altimetry variables in each satellite product Short 10-3 m Daily automated controls are performed and, upon generation, warnings are sent to operators. Quality control reports are also generated on a regular basis once a week. Altimetry experts analyze these reports each week (internal validation, those reports are not disseminated). Section III presents the diagnostics implemented in these reports.. Page 21/ 31

22 III VALIDATION FRAMEWORK The validation aims to control the quality of the external products and the performances of the key processing steps. Different points are assessed by the validation task: The data availability and spatial/temporal coverage the multi-mission inter-calibration and absolute calibration Monitoring of editing statistics Table 6 lists the different metrics that are used. Page 22/ 31

23 Table 6: list of metric for SL-TAC Wave metrics for altimeter-derived measurements Name Description Ocean parameter Supporting reference dataset Quantity L3 SWH_L2-NC AVAIL-<period> Number of altimeter measurements missing/available Significant Wave Height None Missing data are identified over the data flow processed Temporal evolution on the number of measurements on a daily/weekly/monthly basis and/or along each track of the altimeter considered. SWH_L2-NC VALID-<period> Number of altimeter measurements valid/invalid Significant Wave Height None Valid/rejected data are identified over the data flow processed Temporal evolution on the number of measurements on a daily/weekly/monthly basis and/or along each track of the altimeter considered. SWH_L2-NC MEAN_T SWH signal monitoring Significant Wave Height None Temporal evolution on the weekly-averaged significant wave height estimated between +/- 66 latitude estimated over several months for each mission for all/valid data. The associated temporal evolution of the number of all/valid samples should also be attached for mission with high latitude sampling. SWH_L2-NC-ALT-MEAN_T-XOVER Temporal evolution of the weekly-averaged mean difference between two SWH measurements corresponding to altimeter tracks cross-over positions (typically estimated over several months). The performances of the product before and after calibration (inter-calibration, absolute calibration wrt. in situ) are compared. SWH_L2-NC-ALT-CRMSD_T-XOVER SWH differences at monoand multi-missions crossover positions Significant Wave Height None Temporal evolution of the weekly-averaged standard deviation of the difference between two SWH measurements corresponding to altimeter tracks cross-over positions (typically estimated over several months). The performances of the product before and after calibration (inter-calibration, absolute calibration wrt. in situ) are compared. POS_SWH_L2-CLASS3-ALT-VALID- XOVER-<period> Temporal evolution of the weekly-averaged of the number of SWH measurements corresponding to altimeter tracks cross-over positions (typically estimated over several months). Page 23/ 31

24 SWH-M-NC-MEAN-GLB Global map of the averaged along-track SWH (L3) over a month (2x2 grid, for each cell). SWH-M-NC-STD-GLB SWH-M-NC-VALID-GLB SWH signal monitoring Significant Wave Height None Global map of the standard deviation of along-track SWH (L3) over a month (2x2 grid) Global map of number of along-track SWH valid samples (L3) over a month (2x2 grid) SWH-M-NC-REJ-GLB Global map of number of along-track SWH rejected samples (L3) over a month (2x2 grid) L4 SWH-D-NC-MEAN-GLB Global mean of the map SWH (L4) averaged on a daily basis SWH-D-NC-STD-GLB SWH signal monitoring Significant Wave Height None Global standard deviation of the map SWH (L4) on a daily basis SWH-D-NC-VALID-GLB Global number of grid node defined by the map SWH (L4) averaged on a daily basis MERR_SWH-D-NC-MEAN_T-GLB Formal Mapping Error (ERR) monitoring Formal Mapping Error None Global mean of the ERR associated to the map SWH (L4) averaged on a daily basis SWH-D-NC-DFS_MEAN-GLB Contribution of the different altimeters to the map product DFS None Mean contribution of the different altimeters available to the merged map SWH (L4) SWH-M-NC-MEAN-T-GLB Global mean of the map SWH (L4) averaged on a monthly basis SWH-M-NC-STD_T-GLB SWH signal monitoring Significant Wave Height None Global standard deviation of the map SWH (L4) averaged on a monthly basis SWH-M-NC-VALID_T-GLB Global number of grid node defined by the map SWH (L4) averaged on a monthly basis Page 24/ 31

25 IV VALIDATION RESULTS Metrics are described in details in the CMEMS-SL-WAVE-ScVP document. In this section, their application over the time period used for the calibration study is presented. IV.1 Significant Wave Height IV. Data availability over the calibration period Figure 15 presents the application of the data availability diagnosis over the period used for intercalibration between S3-A and J3. The bottom plot represents the missing data over the whole period and also provides information about the last day of the period. Such a diagnosis on the last day is of great interest in the offline validation process that runs every day. Page 25/ 31

26 Figure 15: Data availability for Jason-3 over the calibration period. Top: available data, Bottom: missing data. Blue = whole period, Red = last day IV.1.2 Data editing over the calibration period Figure 16 presents the application of the data editing diagnosis over the whole period used for intercalibration between S3-A and J3 and also provides information about the last day of the period. Figure 17 presents the application of the data editing diagnosis for ice flag and Figure 18 for the thresholds criteria indicated in Table 3. Page 26/ 31

27 Figure 16: Position of the invalid (valid) measurements. Red stands for the last processed day. Figure 17: Position of the measurements invalidated on the ice flag criterion. Page 27/ 31

28 Figure 18: Position of the measurements invalidated on the standard deviation of the range criterion. Page 28/ 31

29 V SYSTEM S NOTICEABLE EVENTS, OUTAGES OR CHANGES No events Page 29/ 31

30 VI QUALITY CHANGES SINCE PREVIOUS VERSION The version presented is the first version of the products. Page 30/ 31

31 VII REFERENCES Sentinel-3 Team, 2013, Sentinel-3 User Handbook v1.0 Aviso+, Along-track Level-2+ (L2P) Sentinel-3A Product Handbook, v1.2, 2016d ( Queffeulou P, and D. Croizé-Fillon, 2017, Global altimeter SWH data set. February Technical report Ifremer. ftp://ftp.ifremer.fr/ifremer/cersat/products/swath/altimeters/waves/documentation/altimeter_wave _merge 11.4.pdf Queffeulou P., OSTST 2016, Validation of Jason-3 altimeter wave height measurements Queffeulou, P., 2012-b, Preliminary assessment of Jason-2 GDR version D for SWH and sigma0 data, September Report available at ftp://ftp.ifremer.fr/ifremer/cersat/products/swath/altimeters/waves/documentation/j2_versions_d_t.pdf Queffeulou, P., and D. Croizé-Fillon. Global Altimeter SWH Data Set, Version 7, May Ifremer, ftp://ftp.ifremer.fr/ifremer/cersat/products/swath/altimeters/waves/documentation/altimeter_wave_merge 7.0.pdf Queffeulou, P., and D. Croizé-Fillon. Global Altimeter SWH Data Set, Version 4, October Ifremer, ftp://ftp.ifremer.fr/ifremer/cersat/products/swath/altimeters/waves/documentation/altimeter_wave_merge 4.0.pdf Queffeulou, Pierre. Long Term Validation Of Wave Height Measurements From Altimeters. Marine Geodesy 27 (2004): doi: / Page 31/ 31