Claudia C. Carabajal1,
                                                                             
                     ...
Globally-distributed Repeated Profiles
                    Geoscience Laser Altimeter System (GLAS)
                   Foo...
•  The high accuracy of the ICESat elevation measurements in
   a consistent reference frame provides a unique, globally
 ...
1A                                                2A       2A
                                      2B                    ...
•  ICESat Land/Canopy Product (GLA14), Release 31
   GLAS waveform-derived elevations
     highest detected signal
     si...
After Harding & Carabajal, 2005.
                    Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 
   6
Stringent editing applied to identify appropriate returns:
     Low within-footprint slope and roughness
     Vegetation a...
•  Negative elevation differences: SRTM biased high relative to ICESat
   absolute datum by several meters, on average, ac...
•  We quantify differences between ICESat GCP’s and SRTM
   along the ICESat ground tracks using a sliding 1 degree box-
 ...
•  Difference histograms for ICESat’s highest, centroid,
               inferred ground and lowest elevations show well-de...
L2A                         L2B                                   L2C




   L3A                         L3D              ...
Along-track    differences  show    large
wavelength     undulations   (100s     of
kilometers) for the various periods, n...
Along-track    differences  show    large
wavelength     undulations   (100s     of
kilometers) for the various periods, n...
Along-track    differences  show    large
wavelength     undulations   (100s     of
kilometers) for the various periods, n...
Residual height error of the
SRTM X-band DEM.

(a)  Error along a particular
     data take acquired over the
     pacific...
points/cell                    mean                               st. dev.


0                1000        -20             ...
Laser 2            Laser 3                     2m




                                                 -2 m




          ...
sparse
                     vegetation
                                                                                   ...
5m

                                                       0m

                                                      -5m

...
Narrow ICESat Waveforms
                                L2B (Feb.-Mar., 2003) 
                        Waveforms       wit...
Identify narrow last peaks in broad waveforms that are likely
  to be returns from the ground beneath the vegetation to
  ...
•  Using careful editing of ICESat elevation data, we are developing a
   Global Geodetic Control database for a variety o...
•  Methodologies developed to use ICESat data for global geodetic
   control purposes are a pathfinder for similar use of ...
Upcoming SlideShare
Loading in …5
×

WE2.L09 - ICESAT LIDAR AND GLOBAL DIGITAL ELEVATION MODELS: APPLICATIONS TO DESDYNI

796 views

Published on

0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
796
On SlideShare
0
From Embeds
0
Number of Embeds
7
Actions
Shares
0
Downloads
17
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

WE2.L09 - ICESAT LIDAR AND GLOBAL DIGITAL ELEVATION MODELS: APPLICATIONS TO DESDYNI

  1. 1. Claudia C. Carabajal1, David J. Harding2, and Vijay P. Suchdeo1 1 Sigma Space Corp. @ NASA/GSFC – Planetary Geodynamics Laboratory 2NASA/GSFC - Planetary Geodynamics Laboratory Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010
  2. 2. Globally-distributed Repeated Profiles Geoscience Laser Altimeter System (GLAS) Footprint: ~70 m (lasers 1 & 2), ~50 m (laser 3) Along-track spacing: 170 m Vertical Precision: 3 cm (flat surfaces) Vertical Accuracy: ~10 cm (flat surfaces) Horizontal Accuracy: < 6 m Primary Objectives Ice sheet elevation change Sea ice thickness change Secondary Objectives Cloud and aerosol profiles Geodetic land topography profiles Forest canopy height sampling Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 2
  3. 3. •  The high accuracy of the ICESat elevation measurements in a consistent reference frame provides a unique, globally distributed Ground Control Point (GCP) data set Vertical Accuracy: 10 cm (flat surface) Horizontal Accuracy: < 6 m •  Three main applications of ICESat geodetic control are: Independent assessment of the accuracy of DEMs defining their random and systematic error characteristics. Correction of systematic errors in DEMs improving their utility scientific and applied purposes including detection of elevation change Use as ground control points in the production of DEMs either by stereo photogrammetric or interferometric SAR techniques Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010
  4. 4. 1A 2A 2A 2B 2C 3A 3B 3C 3D 3E 3F 3G 3H 3I 3J 3K 2D 2E L1 & L2 8-day Laser 2 – 91 day Laser 3 – 91 day Laser Energy Corrected for ICESat was in a precisely Mean per Pulse Energy (mJ) FOV Shadowing Effects repeated orbit (±86°), acquiring data along the same 491 orbit tracks in Laser 3 ~33-day long periods. Laser 2 Laser energy dropped significantly during the Observation Period course of the mission Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 4
  5. 5. •  ICESat Land/Canopy Product (GLA14), Release 31 GLAS waveform-derived elevations highest detected signal signal centroid (average) inferred ground peak lowest detected signal Each Laser 2 and 3 month-long observation periods used separately to assess reproducibility of the results •  SRTM Finished Product DEM elevation interpolated to laser footprint location, provided on GLA14 geoid corrected to be in ICESat reference frame Elevation standard deviation (relief) from 3 x 3 cells at footprint location •  ESA’s MERIS Globcover Global land cover at 300 m resolution (Regional products) 51 land cover classes possible Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 5
  6. 6. After Harding & Carabajal, 2005. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 6
  7. 7. Stringent editing applied to identify appropriate returns: Low within-footprint slope and roughness Vegetation absent or very low stature Not impacted by measurement artifacts •  Surface returns not from cloud tops ICESat - SRTM DEM elevations < 50 m •  Non-saturated returns Saturation index ≤ 2 •  Data acquired near nadir Incidence angle ≤ 1° •  No potential range delay due to atmospheric forward scattering When correction available, in the mm range •  No broadened returns from high relief or vegetation cover Width ≥ 0.5 m and ≤ 5 m Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 7
  8. 8. •  Negative elevation differences: SRTM biased high relative to ICESat absolute datum by several meters, on average, across western Australia. •  The along-profile variations reveal undulating elevation errors in the SRTM DEM at the 100s of kilometer length scale and ~5 m amplitude. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 8
  9. 9. •  We quantify differences between ICESat GCP’s and SRTM along the ICESat ground tracks using a sliding 1 degree box- car filter. •  We compute average 1 degree gridded ICESat-SRTM elevation differences. •  We evaluate spatial patterns of mean elevation differences (biases) and standard deviations (noise component). •  We do this using each ICESat observation period separately, testing the reproducibility of ICESat elevation measurements with different laser energies. •  We include topographic relief and land cover information to establish empirical relationships between ICESat - SRTM elevation differences with respect terrain characteristics. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 9
  10. 10. •  Difference histograms for ICESat’s highest, centroid, inferred ground and lowest elevations show well-defined normal distributions. •  ICESat centroid and inferred ground are essentially equivalent for the narrow waveforms selected by editing •  SRTM elevation bias ~ 2 m above ICESat’s centroid. 15 Frequency (%) 10 Highest Centroid 5 Ground Lowest 0 -10 0 10 ICESat – SRTM Elevation (m) Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 10
  11. 11. L2A L2B L2C L3A L3D L3G The along-profile smoothed differences show long wavelength undulations in the SRTM DEM, of several meters magnitude, that are consistent for all observation periods and lasers. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 11
  12. 12. Along-track differences show large wavelength undulations (100s of kilometers) for the various periods, not correlated with relief. The along-track differences are independent of the ICESat observation period, and are therefore characteristic of SRTM. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 12
  13. 13. Along-track differences show large wavelength undulations (100s of kilometers) for the various periods, not correlated with relief. The along-track differences are independent of the ICESat observation period, and are therefore characteristic of SRTM. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 13
  14. 14. Along-track differences show large wavelength undulations (100s of kilometers) for the various periods, not correlated with relief. The along-track differences are independent of the ICESat observation period, and are therefore characteristic of SRTM. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 14
  15. 15. Residual height error of the SRTM X-band DEM. (a)  Error along a particular data take acquired over the pacific for calibration purposes. Shown is the band of the relative and absolute vertical accuracy requirement. (b) Schematic distribution of SRTM error sources across spatial scales in azimuth direction. The largest error contribution comes from roll angle firings used to counteract the torque exerted on the mast by the earth gravity field gradient. Rabus et al., 2003 Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 15
  16. 16. points/cell mean st. dev. 0 1000 -20 20 0 10 rmse minimum maximum 0 10 -20 20 -20 20 Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 16
  17. 17. Laser 2 Laser 3 2m -2 m -6 m •  Centroid differences for all laser periods show very consistent means of ~ -2m, a demonstration of ICESat’s highly accurate and reproducible absolute elevations. •  There is a slightly decreasing trend with laser energy decay, especially for Laser 2. It is not related to editing of saturated returns during high energy periods. •  The origin of this ICESat L2 drift and the associated increase in standard deviation requires further investigation. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 17
  18. 18. sparse vegetation Water grassland/ cropland/ short grass/ stature shrubs vegetation bare areas grassland/ Cropland/ short grass/ stature shrubs vegetation Bare areas Sparse Vegetation Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 18
  19. 19. 5m 0m -5m Histograms of differences between Mean: -1.91 m ICESat and SRTM 90 m elevations at the St. Dev.: 2.12 m ICESat footprint locations for bare ground land cover. The Mean and Standard Deviation of the distribution are -1.91 m and 2.12 m, respectively, for a population of 46271 laser returns. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 19
  20. 20. Narrow ICESat Waveforms L2B (Feb.-Mar., 2003) Waveforms with narrow pulse-widths (0 to 5 m), are consistent with low relief surfaces having no or only short-stature vegetation cover, and are suitable for use as ground elevation Waveform Pulse Width (m) 5.0 control points. 4.5 4.0 Approximately 30%-35% of the data acquired in North 3.5 America fits this criteria ≤3.0 (however, a large fraction are at higher latitudes where the ground track spacing is smaller). Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 20
  21. 21. Identify narrow last peaks in broad waveforms that are likely to be returns from the ground beneath the vegetation to increase the number of global GCPs. Use of last peaks as GCPs in vegetated terrain must be restricted to areas of low topographic relief due to the complex merging of ground and canopy returns in waveforms from areas moderate to steep relief. (Harding & Carabajal, 2005) Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010 21
  22. 22. •  Using careful editing of ICESat elevation data, we are developing a Global Geodetic Control database for a variety of Solid Earth applications. •  Edited data apply to locations of low relief and absent to short stature vegetation cover (< a few meters). •  As an application of ICESat for Ground Control, we have performed a comprehensive analysis of the spatial distribution and magnitude of the ICESat - SRTM differences for Australia. •  A negative mean difference of ~ 2 m (SRTM on average higher than ICESat) is observed for Australia, but there are regionally correlated mean differences that vary from about -10m to 5m. These might be associated with differences in land cover type. •  We have investigated the repeatability of the results for all ICESat observation periods, exploring possible intra-period instrument/ pointing biases remaining in the ICESat elevation data. •  Identification of ground peaks in broadened waveforms will expand the number of GCPs for vegetated regions. Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010
  23. 23. •  Methodologies developed to use ICESat data for global geodetic control purposes are a pathfinder for similar use of the data to be produced by the Lidar component of the DESDynI mission. •  With substantially improved sampling as compared to ICESat DESDynI will provide a more comprehensive set of global GCPs - Multiple beams spaced across track by ~ 1 km - Smaller footprints (25 m) that are contiguous along track - Continuous, rather than episodic, operation •  Differencing the densely sampled DESDynI Lidar data through time with respect to a common DEM should reveal surface elevation changes at the decimeter level during the course of the mission on a local to regional (TBD) scales, including for surfaces that are decorrelated at radar wavelengths E.G. seasonal snow accumulation; soil loss in agricultural regions Carabajal et al. - IGARSS 2010 - Honolulu, HI, July 25-31, 2010

×