Satellite derived reference surfaces for surveying (VORF, BLAST and LAT) Dr Ole B. Andersen, DTU Space, Copenhagen, Denmark,

Transcription

1 Satellite derived reference surfaces for surveying (VORF, BLAST and LAT) Dr Ole B. Andersen, DTU Space, Copenhagen, Denmark,

2 Who am I. Gravity Author of KMS02/DNSC08/DTU10 high resolution marine geophysical/geodetic maps. 1 minute Global altimetric gravity field map 1 minute Mean Sea Surface height 1 minute Altimetry improved bathymetry Global ocean tide models. Global/regional/Arctic Sea level change(altimetric era). Bathymetry Sea Level Change 2 DTU Space, Technical University of Denmark

3 Overview. Introduction (reference surfaces). Surveys techniques Satellite support Satellite Altimetry and the Mean sea surface. State of the Art Global Ocean tide models. LAT and MSS determination Accuracies / Example Crossing the Gulf Stream BLAST and transformation to local VRF Summary - outlook 3 DTU Space, Technical University of Denmark

4 BLAST EU-7th Interreg FW project 4 DTU Space, Technical University of Denmark

5 BLAST (EU 7th Interreg FW project) The BLAST project has a primary focus on "Bringing Land and Sea Together (BLAST), by harmonizing and integrating on+offshore data. DTU major role is on Transform parameters between different vertical reference systems (VRF) Develop a software tool to implement the transformation between the different VRF s. BLAST IS ONLY DEFINED IN THE NORTH SEA. BLAST METHODS IS APPLICABLE GLOBALLY AND IN THE ARCTIC BLAST IS A DEMONSTRATOR PROJECT. 5 DTU Space, Technical University of Denmark

6 BLAST AND VORF VORF = Vertical Offshore Reference Frame A set of mathematical models of the major surfaces used in the current and future charting A suite of software utilities allowing the transformation of mapping and positioning data between the VORF surfaces UKHO established first demonstrator UK- VORF for Britain in 2007 BLAST established North Sea VORF in DTU Space, Technical University of Denmark

7 Some usages / reasons for VORF? Continuing developments in GPS/GALILEO/GNSS LIDAR and multibeam technology surveyed using GNSS. Analogy with various height reference systems on land International / independent of national Datums (chart) Deal with the increased use of GPS/GNSS-based hydrographic surveys. Applicable to Navigation and ship safety Lowest 7 DTU Space, Technical University of Denmark

8 Surfaces and names: MSL /MSS MLWS LAT Chart Datum (local) GRS80 Ellipsoid 8 DTU Space, Technical University of Denmark

9 Current practice for bathymetric data processing Tide gauge survey vessel Sea Surface observed tide (and derived time) from Use co-tidal chart Tidal correction Issues: Complexity onshore and offshore operations, time Latency the process takes 9 DTU Space, Technical University of Denmark depth measurement (and time of observation) LAT Charted depth time and hence is expensive Accuracy issues co-tidal charts have limited resolution and are derived from limited data; seabed gauges are expensive Inconsistency practices using Chart Datum are sometimes poorly defined Requires transformation into local (oountry) datum of the tide gauge ERRORS in co-tidal charts, transformation etc. or use seabed gauge

10 Bathymetric data processing with BLAST/VORF and GPS survey vessel (+GPS) Sea Surface Tidal correction = h e LAT Tidal correction depth measurement h e LAT Charted depth Charted depth = Depth measurement tidal correction GRS80 Ellipsoid - accessible everywhere 10 DTU Space, Technical University of Denmark

11 Blast/VORF computation method Tide gauge MSS 5km interpolate MSS (altimetry) geoid Altimetric LAT= VORF Altimetric Tidal modelling BLAST approach is applicable to the Arctic. We do have an accurate altimetric MSS (or Mean sea level) We do have accurate Ocean tide model from Altimetry So we can derive an altimetric LAT to be used for surveying This LAT will be in Ellipsoidal reference frame (GPS) 11 DTU Space, Technical University of Denmark

12 How to derive the MSS Satellite Altimetry Ground Tracks ENVISAT TOPEX JASON GFO ERS1/2 12 DTU Space, Technical University of Denmark

13 DTU10 Mean Sea Surface (18 years) Height in GRS80 13 DTU Space, Technical University of Denmark

14 March Arctic -> Ice coverage Decrease in total sea ice extent: September: 11.1 % per decade March: 2.8 % per decade Richter-Menge et al, 2008 September 14 DTU Space, Technical University of Denmark

15 The Arctic Ocean Problems Problems Measurement Periods do not match ICESat covers selected periods CryoSat-2 was launched in 2009 The art is to fit surfaces on each other 1) Reference E1/E2/ENVISAT to TP/J1/J2 2) Reference ICESat to Envisat (same time) 3) Reference CryoSat-2 to ICESat+ENVISAT 15 DTU Space, Technical University of Denmark DTU 10 MSS (height in meters)

16 GPS vs MSS Extrapolation towards the coast is Required for the MSS How accurate is this?? 320 GPS measured Tide Gauges Around Britain. TG MSS (extrapolated) Mean = 1.24 cm (DNSC08) Std = 6.8 cm Upgrading MSS to DTU10 Mean = 0.11 cm (DTU10) Comparison curtesy by Marek Ziebart, UCL London, 16 DTU Space, Technical University of Denmark

17 Getting a LAT from Ocean Tides M2 loop 17 DTU Space, Technical University of Denmark

18 New DTU10 ocean tide model 1. Empirical model based on FES Response method Similar to GOT 4.7 global ocean tide. 3. New satellite data: 18 years of joint TOPEX/Poseidon-Jason-1-Jason-2 mission 4 years of TOPEX-Jason-1 interleaved mission 10 years GFO up to ±72 15 Years ERS-2-Envisat Models 28 tidal constituents including largest shallow water M4 18 DTU Space, Technical University of Denmark

19 19 DTU Space, Technical University of Denmark

20 Run the tide model for 19 years to find minimum (incl Arctic) 20 DTU Space, Technical University of Denmark

21 Ellipsoidal LAT Datum EXAMPLE NORTH SEA (validated) BUT ITS GLOBAL Ellipsoidal LAT surface Based on: DTU10MSS- DTU10OT Relative to WGS84/GRS90 GPS consistent (also Tide system consistent) 21 DTU Space, Technical University of Denmark

22 Accuracy Discussion Errors in altimetric MSS + Tides. Errors in near-coastal extrapolation MSS error ~ 5 cm open ocean Tide error ~ 5 cm open ocean Coastal UK VORF met specs (10 15 cm 1s) across ~80% of inshore and~100% of offshore Increased complexity of tides Shallow water tides. Lack of Altimetric Data (fjords). Worst case scenario could be 1 m. Arctic Issues: ICE Disturbs radar. MSS might be too high by Cm due to sea ice returns. 22 DTU Space, Technical University of Denmark

23 Important Shallow water constituents -> Chart Datum 23 DTU Space, Technical University of Denmark

24 Way forward Extrapolation last 5 km towards the coast What about deep fjords. VORF / BLAST UK VORF demonstrated approach Using 320 UK GPS measured Tide Gauges 2010: UKHO/NAVY initiated global VORF extention using DTU10MSS. 2011: PSMSL initiated global GPS Tide Gauge availability/dtu10integration We now have CryoSat-2 SAR satellites Mearusing closer /accurate to the coast 24 DTU Space, Technical University of Denmark

25 Sea Surface Height (meters) Example DTU10MSS as reference Crossing the Gulf Stream The variability of currents Getting SSH with laser. H antenna (t) = H Laser (t) + H offset H laser (t)=h pitch +H speed +H point +H weight +H bow-wave 2 1,6 1,2 0,8 0,4 0-0,4-0,8-1,2 28, , , , ,5 42 Latitude (degrees) 25 DTU Space, Technical University of Denmark SSH - Tides not removed SSH - Tides Removed DNSC08 MDT - no IB The RMS between LASER and MSS = 17 cm

26 Looking back Integrating with existing reference surfaces (The BLAST project) Data might be in various systems These can be transferred into the same system using BLAST country VD Offset (cm) B DNG -232 (pure leveled heights) D DHHN92 1 (normal heights) F NGF-IGN69-47 (normal heights) DK DVR90 0 (orthometric heights) N NN (orthometric heights) NL NL_AMST / UNCOR +2 (pure leveled heights) UK Newlyn (ODN) (ortometric heights) DTU Space, Technical University of Denmark

27 Offshore framework BE, NL, DK *, NO * survey vessel (+GPS) MSL geoid NO * LAT CD BE FR * NL UK BE (via MSL) DE * FR * NL (via MSL) UK FR * UK ellipsoid * = data partially covers North Sea area of this MS 27 DTU Space, Technical University of Denmark

28 MARINE: VRF program includes the following National LAT / CD datums country LAT CD B Grid No D Grid (part of NS territorial No region) F Available but Outside Available but outside DK Defined by 8 points No Recommend GOT4.7 LAT N Defined by 3 points No Uses GOT4.7 LAT NL Grid No UK Grid Grid All implemented on to common highresblast grid Associated coverage file associated with each grid Informs on reliable coverage 28 DTU Space, Technical University of Denmark

29 Blast transformation program Created a command line Interface program. Development of User interface baced On response from users 29 DTU Space, Technical University of Denmark

30 Outlook Satellite derived MSS and Ocean Tide LAT applicable. Could be established and quality controlled for the Arctic. UKHO UK Navy currently extending VORF with global DTU10MSS UK VORF + BLAST paved the road Must be integrated with local data to enhance local modelleing. Implementing error handling 30 DTU Space, Technical University of Denmark

31 Backup slides - 31 DTU Space, Technical University of Denmark

32 Arctic Ocean TPX 7.2 vs GOT 4.7 DTU10 vs GOT DTU Space, Technical University of Denmark

33 BLAST Reference surface EGG02008 Geoid (N) Numbers are GPS levelling height Hellip-Hlevel-N Clear tilt in the UK Levelling data. 33 DTU Space, Technical University of Denmark

34 EVRF-EGG Transformation The EVRF2007 based surfaces (land) will be Tranformed via the the EGG08 geoid. The surface EVRF-DIF has been modelled to handle this. And this is implemented in the BLAST program. 34 DTU Space, Technical University of Denmark

35 BLAST LAT surface Based on DTU10 Ocean tide model Identical to within 5 cm of GOT4.7 ocean tide model 35 DTU Space, Technical University of Denmark

36 Blast transformation program Input / Output Input specify which country and system you are in #The data is as follows: #ID lat lon h country system pt hgt DTU Space, Technical University of Denmark

37 MSS from Satellite Altimetry 37 DTU Space, Technical University of Denmark

38 The DNSC08 Mean Sea Surface Want complete coverage in space and time Get the best out of ERM (Variability averaged out) and GM (high spatial resolution) First purely Geometrical MSS Mean period Derived from T/P, T/P TDM, ERS1 ERM+GM, ERS2 ERM, ENVISAT, Geosat GM, GFO Total 12 years of data using T/P + Jason-1 as reference The MSS has been derived in the Mean Tide System NEW!!!! DTU10 Available Mean Vertical Accuracy 4-6 cm deep ocean best - less accurate close to coast Model (Name) T/P data Years Res KMS04 CLS01 GSFC00/00.1. KMS01 NCU01 GSFC98 CLS-SHOM 98, KMS98 CSR95 OSU95 9 (93-01) 7 ( (93-99) 7 (93-00) 6 (93-98) 3 (93-95) 3 (93-95) 3 (93-95) 2 (93-94) 1 (93-93) DTU Space, Technical University of Denmark MSS = MDT + Geoid

39 MDT (DNSC08MSS-EGM2008 = DNSC08MDT) 39 DTU Space, Technical University of Denmark

40 Sea Surface Height (meters) GPS PPP processing TIDE SYSTEMS GPS TIDE FREE!!!!!!! H antenna (t) = H Laser (t) + H offset H laser (t)=h pitch +H speed +H point +H weight +H bow-wave 2 1,6 1,2 0,8 0,4 0-0,4-0,8-1,2 28, , , , ,5 42 Latitude (degrees) 40 DTU Space, Technical University of Denmark SSH - Tides not removed SSH - Tides Removed DNSC08 MDT - no IB

41 A good MSS and Geoid -> Good MDT MDT = DNSC08MSS NAT04G 41 DTU Space, Technical University of Denmark

42 DNSC08MSS-LAT47 (Ref to GRS80) 42 DTU Space, Technical University of Denmark