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A Merged Global Digital    Jet Propulsion Laboratory Topographic Data Set     California Institute of Technology
A Merged Global Digital    Jet Propulsion Laboratory Topographic Data Set     California Institute of Technology
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A Merged Global Digital Topographic Data Set - Progress Report.pdf

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A Merged Global Digital Topographic Data Set - Progress Report.pdf

  1. 1. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology IGARSS 2011 Dr. Michael Kobrick Dr. Robert Crippen Dr. Thomas FarrJet Propulsion LaboratoryJuly 27, 2011
  2. 2. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of TechnologyObjective: Generate best quality global digital elevation data set at highest possible resolution by combining best existing dataSupported by NASA *MEaSUREs program (M. Maiden)for enhancement of SRTM data set * Making Earth Science Data Records for Use in Research Environments
  3. 3. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology SRTM: Shuttle Radar Topography MissionMission• Partnership between NASA, NGA, DLR and ASI• C-band single-pass interferometry• X-band interferometer by German and Italian space agencies• Mission duration: Feb., 11 – Feb. 22, 2000 (11 days, 5 hours) Objective • Produce DEM of 80% of Earth surface ! 30 meter posting ! Complete coverage ± 60° latitude ! WGS84 EGM96 geoid datum ! 16 m vert., 20 m horiz. accuracy at 90% level
  4. 4. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Topographic Coverage • DTED1 coverage • 90 meter samples • ~ 60% coverage • Poor continuity• SRTM coverage• 30 meter samples• ~ 80% coverage• Excellent continuity
  5. 5. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Accuracy results Accuracy tests • NGA verification with DTED, other data sources • USGS comparisons to National Elevations Data sets, GPS arrays • Comparison to static and dynamic GPS elevations • Scores of open literature reports comparing to local data sets All show data exceed 16 m vertical accuracy specs by factor of ~3Elevations clearly show patterns of tropical forestclear-cutting with height differences of 4-5 meters
  6. 6. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of TechnologyData distributed by Land Processes DAAC at EDC 567809&0&,+:;<+,=&>9*?4,/, *"/,#@"%-()&=3(#&0,)=!"#$%&4(0/+(-$/&= AB:/"-&+CDEFCFG5$)&HFDEFCCI (*!!!*!!!# )"!# *(!!*!!!# ("!# *!!!*!!!# &*(!!*!!!# !"#$%&()*&+,-./&0 "!# 1$%-&+"23(#&0 &*!!!*!!!# %*(!!*!!!# &"!# %*!!!*!!!# %"!# $*(!!*!!!# $*!!!*!!!# $"!# (!!*!!!# !# !"!# +,-.$!# /01.$!# 23,.$!# 456.$$# 738.$$# 95:.$$# ;<:.$$# 95=.$$# 4>6.$$# 4,/& 7?@3A#20B6@05C3C# D0@>E3FGHI#
  7. 7. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Data RestrictionsRe original NASA/NGA Memorandum of Understanding, DEMs better than 3 arcsec outside U.S territory may not be distributed outside NASA3 arcsec DEMs and any derived, ancillary or associated products may be distributed at any resolution, as long as they cannot be reverse-engineered to better than 3 arcsec DEMs
  8. 8. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology NASA MEaSUREs ProgramUnder MEaSUREs NASA has funded effort to create SRTM-derived,enhanced, merged global data set! • Void filled DEMs! • Enhanced DEM control using ICESat profiles! • Individual and mosaiced radar image data! • Raw radar and ancillary data set
  9. 9. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology NASA MEaSUREs ProgramNASA has funded effort to create SRTM-derived, enhanced, mergedglobal data set! • Void filled DEMs! • Enhanced DEM control using ICESat profiles! • Individual and mosaiced radar voids - cell average 0.52%, median 0.0023% SRTM image data! • Raw radar and ancillary data set
  10. 10. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Many SRTM DEMs have voids• Voids (areas with no data) caused by high slopes or extremely low SNR• Can be filled with supplementary DEMs SRTM voids - cell average 0.52%, median 0.0023% Original SRTM Voids filled with ASTER DEM
  11. 11. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Potential Void Fill Sources NED !• National Elevation Data (NED), 30m - Excellent quality - Available only for U.S., Mexico• Canadian Digital Elevation Data (CDED), ~ 20m - Available for virtually all of Canada CDED• Other sources - various resolutions - SRTM / X-SAR - TanDEM-X - SPOT - Australian GEODATA Topo X-SAR• ASTER GDEM - Excellent coverage - Matches SRTM geoid, format, sampling - Some voids and artifacts
  12. 12. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology GDEMWith NASA support Silcast Corp. processed several million ASTERstereo pairs to produce a global DEMGDEM1 released in mid-2009 - Matches SRTM in posting, datum, formatting - Coverage exceeds SRTM - Resolution ~ 120m, versus 50-60m for SRTM - Numerous artifacts due to cloud mask, stacking methodGDEM2 to be released in mid-2011 - Resolution improved by using smaller convolution kernel - Many artifacts remain
  13. 13. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology GDEM coverage SRTM coverage
  14. 14. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology GDEM2 - SRTM Global Land Cover EGM96
  15. 15. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology ComparisonSRTM ASTER GDEM GDEM1
  16. 16. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology ComparisonSRTM GDEM1
  17. 17. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of TechnologySRTM w/ void GDEM1
  18. 18. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of TechnologySRTM GDEM1
  19. 19. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of TechnologySRTM ASTER GDEM1
  20. 20. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology GDEM includes ancillary NUM file showing number of pairs contributing to each sampleSRTM GDEM1 GDEM Num Capetown area, South Africa
  21. 21. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology GDEM2 ImprovementGDEM1: Original version delivered mid-2009 - Suffered from low resolution (~120 m), cloud and data stacking induced artifactsGDEM2: Beta version being evaluated now - Improved resolution with smaller convolution kernel, many artifacts remain - Included quality files allow identification of most(?) artifacts SRTM GDEM1 GDEM2 GDEM2 N>2
  22. 22. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology NUM = 3• Voiding samples with NUM < 3 seems to eliminate most artifacts• Deletes ~ 7% of GDEM samples• GDEM2 and SRTM voids only loosely correlated Distribution of NUMs in GDEM2
  23. 23. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Voids SRTM GDEM2 N>2 SRTM/GDEM2 Combo
  24. 24. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology NASA MEaSUREs ProgramNASA has funded effort to create SRTM-derived, enhanced, mergedglobal data set! • Void filled DEMs! • Enhanced DEM control using ICESat profiles! • Individual and mosaiced radar image data! • Raw radar and ancillary data set
  25. 25. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology ICESat Data • Comparisons of ICESat profiles w/ SRTM data have revealed possible bias at latitude extremes • Other published work suggests possible SRTM bias in high elevationMalaspina glaciated terrain (this deserves more attention) • SRTM ocean residuals (should center on zero) show curious latitude dependence • Residuals are well within accuracy specs, but systematic nature is obvious • Important to study of glacier changes with implications for climate change SRTM ocean residuals from unedited data Residual latitude dependence
  26. 26. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology ICESat Data• M. Simard working with Carabajal, Sauber et al at GSFC to develop database of ICESat topographic profiles for additional ground truth• Requires careful modeling of laser echoes, differentiation of vegetation, bare Earth returns• Will be applied as additional ground control for void-filled DEMs• Processing using new control data to begin mid-2011
  27. 27. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology ‘Bonus Data’• Rasterized version of SRTM Water Body Data (significant improvement to World Vector Shoreline) - complete, ~15000 ESDRs to be shipped Aug., 2011
  28. 28. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Void-filling Summary• Plan as proposed: Void fill SRTM on best effort basis (~20% of tiles)• GDEM1 available: Void fill much of SRTM with manual artifact detection• GDEM2 available: Void fill most of SRTM with semi-automated artifact detection• Will allow data generation greatly exceeding original MEaSUREs plan and• Expanded plan...
  29. 29. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Expanded Plan• Original NASA-NGA MOU has expired, creating possibility of distributable full- resolution data set• At NASA request generated set of options for SRTM data “reprocessing”• A task plan for an expanded effort is now under review at NASA Hq• Plan will involve additional resources and an additional year beyond end of MEaSUREs program in 2012• Resulting data set to be called NASADEM
  30. 30. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Elements of NASADEM• First step is interferometric reprocessing of SRTM raw data with improved algorithms, faster computers - Better handling of Beam Adaptive Tracker and other ancillary data - Improved phase unwapping algorithms - Leverage NASA ʻCloudʼ computing resources• ICESat database will provide vastly improved ground control• GDEM2 quality incorporating NUM files is sufficient to merge (not just void-fill) with SRTM, most voids will disappear• Remaining voids will be filled with new ASTER acquisitions or other data sets - EDC has agreed to provide additional ASTER DEMs as required from archive or new acquisitions - R. Crippen has developed technique for detecting and eliminating artifacts in individual ASTER DEMs• SRTM water mask will allow incorporation of NGA coastline and other water body information
  31. 31. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Raw radar echoes NASADEM ASTER GDEM2 Artifact removal SAR processing (updated) Current SRTM Modified GDEM2 Global DEM Updated strip DEMs Void-fill SRTM Metric Data Continental Adjustment (mostly) void- Remaining IceSAT filled SRTM (ver3) void map Data Set Acquire new ʻNewʼ SRTM Global DEM NED, CDED, et al LPDAAC ASTER DEMs New ASTER DEMs SRTM Water Body Data Modified DEMs Artifact removal Merge corrected DEMsKey: Pink: New data set or process NASADEM + associated products:Yellow: Existing data set or process Slope, Aspect, Curvature, Images, Process Errors, Correlation
  32. 32. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Elements of NASADEM• Data will be distributed and freely available at full 30 meter posting!• New data types included - Correlation maps - Error metrics - Terrain corrected images, slopes, et al• Processing will be continent-by-continent, with release throughout latter half of 2013
  33. 33. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology NASA MEaSUREs ProgramNASA has funded effort to create SRTM-derived, enhanced, merged 50.02aglobal data set 151.07d! • Void filled DEMs! • Enhanced DEM control using ICESat profiles! • Individual and mosaiced radar image data! • Raw radar and ancillary data set
  34. 34. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Radar Image Task StatusBasic Image Set• Includes image, incidence angle map for each subswath crossing each cell• Subswath inclusion allows differentiating polarizations• Numerous files/cell, total data set ~ 700 gigabytes (compressed!)• Distributable at 1 arcsec• Complete: > 365,000 ESDRs en route to Land Processes DAAC Data take number (may be from 2 to ~20) 34.02a 50.02a 135.07d 151.07d Images Individual data take (per subswath) stacks for each cell incidence angles
  35. 35. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology SRTM Image Data Example ApplicationImage Incidence angle User-definedregion of interest Scatter plot generates backscatter curve
  36. 36. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Radar Image Task StatusCentral Canada Single-swath mosaic Average of all swaths
  37. 37. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology Radar Image Task Status GILF KEBIR TM SRTM
  38. 38. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology SRTM Radar Image of Lake Baikal
  39. 39. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology
  40. 40. A Merged Global Digital Jet Propulsion Laboratory Topographic Data Set California Institute of Technology

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