SRTM DATA PROCESSING STATUS James A' Slater

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SRTM DATA PROCESSING STATUSJames A. Slater
2004 Consolidated Army Topographic, Terrain
Analysis and Multispectral Imagery Conference
(CATTMIC) Ft. Belvoir, VA, 26 May 2004
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OUTLINE

• Review of SRTM Mission Characteristics
• Data Acquisition Completeness
• SRTM Data Products and Data Finishing
• Current Production Status
• Filling Voids in Finished SRTM DTED
• Accuracy Evaluation
• Data Release Policy

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SRTM MISSION CHARACTERISTICS

• NASA SPACE SHUTTLE ENDEAVOR ORBITER STS-99
• LAUNCH DATE 11 FEBRUARY 2000
• INTERFEROMETRIC SYNTHETIC APERTURE RADAR SYSTEM
  (IFSAR) - SINGLE PASS
• C-BAND RADAR (JPL) AND X-BAND RADAR (DLR)
• ADDITIONAL SPONSORSHIP - ITALIAN SPACE AGENCY
  (ASI)
• 11-DAY MISSION COVERING 159 ORBITS BETWEEN 60º N
  AND 56º S LATITUDES

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DATA COLLECTION SUMMARY

• 80 OF EARTHS LAND MASS ( 60º N TO 56º S )
• 99.96 COVERED ONCE AND 94.59 COVERED TWICE

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PERCENT COMPLETE DATA FINISHED CELLSNORTH AND
SOUTH AMERICA
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DATA ACQUISITION COMPLETENESSWESTERN EURASIA
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DATA ACQUISITION COMPLETENESSEASTERN EURASIA
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DATA ACQUISITION COMPLETENESSAFRICA
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SRTM DATA PRODUCTS

• Digital Terrain Elevation Data (DTED) Levels 2
  And 1
• Uniform matrix (1 arc sec spacing and 3 arc sec
  spacing) of terrain elevation values
• Accuracy spec For DTED 2 16 m Vertical, 20 m
  Horizontal (90)
• Orthorectified Image Mosaic (OIM)
• 30 m ground sample distance SAR image mosaic
• Ascending and descending passes
• Terrain Height Error Data (THED)
• Random error of the SRTM DTED
• Seam/Hole Composite Map (SHCM)
• Color-coded raster map of boundaries of seams and
  voids in strip image data
• SRTM Water Body Data
• Vector file of ocean and inland water body
  shorelines

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DIGITAL TERRAIN ELEVATION DATA (DTED) GENERAL
CHARACTERISTICS

• Uniform matrix of elevation values indexed to
  specific points on the ground
• Collected, processed and stored in 1-degree x
  1-degree Cells
• Each cell 100 km (60 nautical miles) on a side
  (at the equator).
• Water body heights edited
• Lakes (600 m length minimum) are leveled
• Rivers (183 m width minimum) are monotonically
  stepped down
• SRTM No. of Elevation Data Interval
  Accuracy Specifications
• DTED Measurements (Horiz. Spacing)
  Absolute Relative Absolute
• Level Per Cell (arc seconds)
  Vertical Vertical Horizontal
• 1 1.4 million 3
  16 m 10 m 20 m
• 2 13 million 1
  16 m 10 m 20 m
• Note Applies to 50ºN to 50ºS latitudes spacing
  increases between 50-70º
• latitudes 1 arc second 30 m at equator.
• 90 linear vertical error and 90 circular
  error for horizontal accuracy.

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SRTM DTED CHARACTERISTICS

• Reflective Surface
• Vegetation canopy
• Some man-made features
• Partial Cells
• Shadows and layover
• Error Estimate for Each Elevation Post in
  Separate File
• SRTM DTED 1 Derived from DTED 2
• Identical values at 3 arc sec (90 m) post spacing
• Horizontal Datum - World Geodetic System 1984
  (WGS 84)
• Vertical Datum - Mean Sea Level as determined by
  WGS 84 Earth Gravitational Model (EGM 96) Geoid

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SRTM DATA PROCESSING

• JPL Raw Data Processing (14,353 cells)
• Completed in Jan 03 and delivered to contractors
  for finishing
• Contractor Finishing Processing (Sep 02 Sep 04)
• BAE (w/ Vexcel)
• Boeing Autometric (w/ Intermap Technologies)
• 40 operators at each contractor
• Follow-on Void-Fill Contract (May - Dec 04 and
  beyond)
• Boeing
• Select, prioritized subset of data

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DATA FINISHING TASKS

• Quality Assurance of JPL Data Products
• Detection and Elimination of Spikes/wells
• Interpolation of Small Void Areas (16 pixels or
  less) Only
• Editing Elevation Data to Correctly Portray Water
  Bodies (lakes, rivers, ocean shorelines) in DTED
• - Automated methods developed by contractors to
  detect
• and delineate shorelines and compute water
  elevations
• using radiometric intensities from ascending
  and
• descending OIMs, Landsat-derived water
  mask,and terrain
• height errors
•   

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SRTM PRODUCTION STATUS
FINISHED SRTM DATA STATUS AS OF 30 APRIL 2004
TOTAL NO. COMPLETION FINISHED
TO DATE CONTINENT OF CELLS DATE NO.
PERCENT S. America
1,807 Jun 03 1,807 100 N. America
2,290 Apr 04 2,290
100 Eurasia-West 2,626 Apr 04 2,565
98 Eurasia-East 3,108 Apr 04
2,558 82 Australia 1,062 Aug
04 20 2 Islands 141
Aug 04 0 0 Africa
3,249 Sep 04 1,173 36 Total
14,283 10,413 73 85º E
longitude is dividing line between East and West
Eurasia.
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SRTM PRODUCTION FINISHING STATUSNORTH AND SOUTH
AMERICA
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SRTM PRODUCTION FINISHING STATUSWESTERN EURASIA
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SRTM PRODUCTION FINISHING STATUSEASTERN EURASIA
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SRTM PRODUCTION FINISHING STATUSAFRICA
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SRTM ELEVATION CONTOURS FOR VOLCANO IN CELLS
W025N14 W025N15(40m contour interval, voids
not filled)
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TEST AND EVALUATION CELLS
45N
Test and Evaluation Site. (TE) The following
TE site location was selected from the North
American Continent data set. The 5 cell by 5
cell array selection was based on its diverse
terrain and hydrology. As noted BAE Systems was
awarded the North American continent and thus had
a different delivery schedule, and
therefore, Autometric began finishing these
cells sooner. The three cells, outlined in red,
were selected to illustrate the diverse terrain,
hydrology conditions, and the contractors
different finishing approach, based on
these conditions and the various NGA provided
sources.
40N
77W
72W
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TEST AND EVALUATION CELL W077N44
Landcover
JOGA (1250,000)
Note No Landcover provided over Canadian
territory (area to the left of red line).
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TEST EVALUATION CELL W077N44 ORTHORECTIFIED
IMAGE MOSAICS
DOIM
AOIM
Note Black may indicate no information.
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TEST EVALUATION CELL W077N44 TERRAIN SHADED
RELIEF OVERLAID WITH WATER FEATURES (blue)
Autometric Solution
BAE Systems Solution
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TEST EVALUATION CELL W077N44 HORIZONTAL WATER
DIFFERENCE
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TEST EVALUATION CELL W077N44 WATER ELEVATION
DIFFERENCE (m) (Autometric minus BAE)
Range -4m to 5m
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SRTM VOIDS

• SRTM DTED Void Characteristics
• JPL achieved project objectives of 95 global
  coverage
• Single 1x1 degree cells may have significantly
  higher voids
• Voids are typically related to radar shadow in
  high relief, or low signal return in low relief
  (usually water/coastal swamp or dry sand)
• Voids are typically shotgun pattern in nature
• Data immediately surrounding void may be noisy
• Void-Fill Project
• Plan initiated to fill voids in 2,000 cells this
  calendar year and additional increments over next
  3 years
• Methodology developed by contractor to
  systematically fill voids in finished SRTM DTED
  with variety of data sources or interpolation on
  a priority basis after current finishing work is
  completed
• Related terrain height error data files and
  possibly other products to be updated concurrent
  with the DTED void fill.

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NOT ALL VOID FILL GIVESVALUE-ADDED RESULTS
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KINEMATIC GPS TRANSECTSFOR SRTM EVALUATION
Note Transect alignments are approximate.
2 Aug 2001
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KINEMATIC GPS GROUND CONTROL POINT COMPARISON
WITH SRTM
Unpublished results, E. Rodriguez et al., JPL,
May 21, 2003. Mean differences SRTM-GPS.
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COMPARISON OF SRTM ELEVATIONS WITH REFERENCE DTED
Mean Difference Reference DTED - SRTM
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DATA RELEASE POLICY

• All SRTM Data Unclassified
• Restrictions Apply to Release
• Public Data
• World-wide DTED 1 (3 arc sec spacing)
• U.S. DTED 2 (1 arc sec spacing)
• World-wide Strip Radar Imagery at 30 m Resolution
• U.S. Phase History Data (raw data from flight)
• Distributed by USGS EROS Data Center

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SRTM PROGRAM STATUSSUMMARY

• Production Status
• JPL part of processing complete (14,353 cells)
• Over 10,400 cells finished as of 30 April 2004
• North and South America and Eurasia completed
• 94 of cells in N and S America have less than 1
  voids
• Africa and Australia to be completed by Sept 2004
• Access to Finished SRTM Data Products
• NIMA Gateway via JWICS or SIPRnet
• USGS EROS Data Center (public data only)
• Not available from DLA yet
• Void-Fill Project underway to fill voids in
  selected, prioritized subset of approximately
  2,000 cells
• Absolute elevation data accuracy appears to be
  significantly better than 16 m specification