InSAR and LIDAR Lecture 9 Oct 30, 2007

1. Interferometric Synthetic Aperture Radar (InSAR)  Is a process whereby radar images of the same location on the ground are recorded by Two antennas of one platform separated by a few meters (single pass), or The same radar system at different times (multi-pass or repeat-pass)  Applications on Elevation (DEM) derivation (single or multi pass)  Can be as accurate as DEM from traditional optical photogrammetric techniques. However, InSAR operate through clouds, day or night.  The first worldwide DEM (99.97%) was acquired in 2000 by SRTM in 2000, not by the photogrammetry Surface displacement study (multi-pass only)

Examples  One SAR with 2 antennas (single-pass) AIRSAR/TOPSAR  Along track interferometric mode (ATI) (L and C) Ocean current and waves  Cross track interferometric mode (TXI) (L or C) DEM (3-5 m or 1 m) Shutter Radar Topographic Mission (SRTM)  C band and X band antennas separated by 60 m  One SAR in different times (multi-pass) SIR-C ERS 1,2

Phase shift =  is the fractional phase (value 0-2  radians), λ is wavelength

Calculate altitude (1) (2) (3) (4)  is the fractional phase (value 0-2  radians), λ is wavelength

AIRSAR/TOPSAR  Operates from a NASA DC-8 jet. When AIRSAR is used to create topographic map (DEM), it is called TOPSAR.  Fully polarimetric imagery (HH, VV, HV, VH) in three bands: C (5.6 cm, 5.26 GHz) L (24 cm, 1.22 GHz) P (60 cm, 0.45 GHz)  Spatial resolution of 10 m for 20 MHz radar data and 5 m for 40 MHz data. Multilook post-processing can be applied to the radar imagery to reduce speckle at the expense of decreased spatial resolution

Xie, 2002; Xie and Keller, 2006

 Glaciers are sensitive indicators of climatic change. They can grow and thicken with increasing snowfall and/or decreased melting. Conversely, they can retreat and thin if snowfall decreases and/or atmospheric temperatures rise and cause increased melting. Landsat imaging has been an excellent tool for mapping the changing geographic extent of glaciers since The elevation measurements taken by SRTM in February 2000 now provide a near-global baseline against which future non-polar region glacial thinning or thickening can be assessed.

Source for SRTM data  USGS gallery: gahttp://srtm.usgs.gov/srtmimagegallery/index.html  JPL gallery:  USGS seamless distribution system (USA 30 m, globe 90 meter)

SRTM coverage map To download from here

Displacement  Interferogram of Landers earthquake 7.3 magnitude on June 18, This is a remarkable new tech gained recognition thereafter.  This is from ERS-1  Average displacement along the fault rupture was 3-4 m, maximum was 6m.  Each color cycle represents additional 2.8 cm ground motion or displacement.

2. LIDAR  LIght Detection And Ranging uses the same principle as RADAR. The lidar instrument transmits laser out to a target. The transmitted light interacts with atmosphere and target. Some of this light is reflected / scattered back to the instrument where it is analyzed.  Use UV, visible, and infrared  Transmitter (laser), receiver, and detector  Distance = C x T /2  Four types Ranger finders: it is the simplest lidars, it measures the distance, then create the topographic map DIAL: Differential Absorption Lidar is used to measure chemical concentrations (such as ozone, water vapor, pollutants) in the atmosphere. Doppler Lidars: it’s used to measure the velocity of a target Raman LIDAR: can measure gaseous species

Airborne Lidar System ALTMS (TerraPoint, USA) FLI-MAP (John Chance, USA) ALTM (USA) TopoEye (USA) ATLAS (USA)

Lidar elevation data of Bristol, UK

 These data are collected with aircraft-mounted lasers capable of recording elevation measurements at a rate of 2,000 to 5,000 pulses per second and have a vertical precision of 15 centimeters (6 inches). After a baseline data set has been created, follow- up flights can be used to detect shoreline changes.

Surface and DTM

DSM and DTM DSM DTM (bare)

Airborne Lidar

 DIAL laser measures water vapor, clouds, and aerosols by comparing the absorption and scattering of different laser pulses on these atmospheric species

ICESat  The first LIDAR satellite for Earth launched 1/12/2003 The Ice, Cloud, and Elevation Satellite (ICESat) The Geoscience Laser Altimeter System (GLAS)  Two wavelengths: 532 nm and 1064 nm 532 nm channel: vertical distribution of clouds and aerosols 1064 nm channel: surface elevation of ice sheets and sea ice thickness, 15 cm in accuracy.

CALIPSO  Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), launched 4/28/2006.  Provide a global set of data on aerosol and cloud properties, radiative fluxes, and atmospheric state.  Equipment: Lidar: 632 nm and 1064 nm Radiometer Camera 

Calipso instrument

MOLA  Mars Orbiter Laster Altimeter (MOLA), the first satellite-based Lidar system, launched on November 7, 1996 on board the Mars Global Surveyor.  Wavelength 1064 nm, 130 m footprint and 330 m along track spacing (vary with latitude)  To construct a precise topographic map of Mars Mars’ south pole has a higher elevation than the north pole by ~6 km. N S