Principles of Remote Sensing. Shuttle Radar Topography Mission S R T M. Michiel Damen. Dept. Earth Systems Analysis

Transcription

1 Principles of Remote Sensing Shuttle Radar Topography Mission S R T M Michiel Damen Dept. Earth Systems Analysis

2 Contents Present problems with DEMs Advantage of SRTM Cell size Mission and system Radar Interferometry Downoad and import of SRTM data 2

3 Present availability topographical maps 1: : : : % % % % Africa Asia Australia Europe N. America S. America Source: CNES, Paris/Toulouse, 1997 (From PowerPoint Ben Maathuis, ITC

4 Present problems with DEMs Elevation derived from the interpolation of topographic contours is not always accurate enough because of loss of detail Electronic theodolites and GPS provide only point measurements Integration of topographic data from different sources may result in inhomogeneous data quality due to different datums, map projections, formats, resolutions, etc. (Maathuis, ITC) Text after PowerPoint B. Maathuis, ITC

5 Advantage of SRTM Homogeneity: SRTM DEM has not been mosaiced from data derived from different sensors, formats and dates Resolution improvement: only spatial resolution of approx. 90 m. and vertical accuracy of < 10 m. In US even 30 m! Freely available from the internet Text after PowerPoint B. Maathuis, ITC

6 Cell size of DEM Resolution: cell size of approx. 92 m and vertical accuracy of < 15 m. Cell size in US even 30 m! Text after PowerPoint Maathuis, ITC Figures: USGS SRTM Website

7 Cell size of DEM GLOBEDEM SRTM Global SRTM USA 1 km 90 m 30 m Figures: USGS SRTM Website

8 Mission and System 1 Space Shuttle flight of 11 days; launched 11 February 2000 Radar instrument: Spaceborne Interferometric SAR with a 60 m. long mast and X-band (3.1 cm) and C-band (5.3 cm) antenna Text after PowerPoint B. Maathuis, ITC Figures: USGS SRTM Website

9 Mission and System 2 Space Shuttle with 60 m. long SRTM mast Pictures: USGS SRTM Website

10 Mission and System 3 Radar beam swath width 225 km; orbit altitude 233 km. Day, night and all weather independent Text after PowerPoint B. Maathuis, ITC Figure: USGS SRTM Website

11 Radar Interferometry 1 The technique to generate three-dimensional images from the Earth s surface by combining two sets of radar signals. A transmit antenna illuminates the terrain with a radar beam which is scattered by the surface. Two receive antennas with a fixed separation between them (baseline) record the backscattered radar echo from slightly different positions. Baseline Transmitted wave Received wave Text and figure: USGS SRTM Website

12 Radar Interferometry 2 The baseline distance between the main antenna and the outboard antenna were known very accurately and remained constant. What did change is the distance to the Earth's surface in relation to the two antennas. Within the reflected radar beam, the point which represents where the reflection took place was slightly different between the main and outboard antennas. Baseline Transmitted wave Received wave Text and figure: USGS SRTM Website

13 Radar Interferometry 3 Using the information about the distance between the two antennas and the differences in the reflected radar wave signals, accurate elevation of the Earth's surface can be calculated. When two interferometric radar data sets are combined the first product made is called an interferogram. This looks similar to those bands of color you see in a film of oil. Text and figure from USGS SRTM website

14 Radar Interferometry 4 See also web slide Text and figure from USGS SRTM website

15 Download of SRTM data Text and figure from USGS SRTM website

16 Download of SRTM data Freely available from the internet : ftp://e0srp01u.ecs.nasa.gov/srtm/version2/ Blocks of 1 x 1 degree

17 Download of SRTM data ftp://e0srp01u.ecs.nasa.gov/srtm/version2/ Text and figure from USGS SRTM website

18 Download of SRTM data ftp://e0srp01u.ecs.nasa.gov/srtm/version2/ Topographic Open Topographic SRTM DEM File Save File As Tiff/GeoTIFF

19 Download of SRTM data Seamless 1. View and download International data Text and figure from USGS SRTM website

20 Download of SRTM data Seamless Downloads 4 Green selection OK 2 3 SRTM Finished 3 arc sec Text and figure from USGS SRTM website

21 Download of SRTM data Seamless Modify Data Request 5 6 Text and figure from USGS SRTM website

22 Import SRTM data in ENVI File Open Image File File Save File AS Tiff/GeoTIFF Topographic Open Topographic SRTM DEM

23 Hillshaded SRTM DTM from Bali, Indonesia Image processing: Ben Maathuis, ITC

24 Questions