RADAR (RAdio Detection And Ranging)
CLASSIFICATION OF NONPHOTOGRAPHIC REMOTE SENSORS PASSIVE ACTIVE DIGITAL CAMERA THERMAL (e.g. TIMS) VIDEO CAMERA MULTI- SPECTRAL SCANNERS VISIBLE & NIR MICROWAVE Real Aperture HYPERSPECTRAL (e.g. AVIRIS) SLAR Synthetic Aperture LASER (LiDAR) ACROSS TRACK (sweep) e.g. Landsat, AVHRR ALONG TRACK (push) e.g. SPOT
Electromagnetic Spectrum Letter codes not alphabetically linked to wavelength size 5.7cm 23.5cm 58cm
Operation of imaging radar Active sensor with own radiation source The antenna acts as both transmitter and receiver (a circulator switch helps to switch roles) Radar pulses are transmitted at constant intervals and radar echo is received Wave amplitude, phase, and time of travel are recorded (time of travel is an indication of the distance of target)
Radar Characteristics Synthetic Aperture (SAR) versus Real Aperture Radar (RAR) Resolution (Azimuth, and Range) Frequency or wavelength (X, C, L, P) letter codes are carryover from military to civilian applications- codes not related to wavelength size Polarization (HH,VV, HV/VH)- the geometry of how radar pulses are sent and received
Radar advantages: Cloud and smog free data (wavelengths of million times optical wavelengths) Night vision Forest penetration reveals sub-canopy features using longer radar wavebands (for example, L and P bands) Complements visible/infrared sensors (sensitive to terrain features) Good for discrimination of geology and terrain structure (roughness) Radar disadvantages: Interpretation requires knowledge of radar interaction with surfaces Speckle (dark and bright pixels) limits interpretation Not multispectral (one band/one polarization) on most satellite platforms Not good for discrimination of different vegetation types
Radar image of columns of M47 tanks Tank Radar Shadow Trees Road
Central American Region 1996 JERS-1 HH, L-band, 25 m 300+ image mosaic
Reflector Surfaces Specular HH Corner HV Diffuse
BACKSCATTER INTENSITY Radar Image Formation DEPRESSION ANGLE DOUBLE BOUNCE GROUND RANGE SPECULAR TARGET Diffuse Target SHADOW TIME GRAY SCALE
Polarization (like pole-hh, VV or cross pole- HV, VH send and receive signal) X Electric Field (Vertically polarized wave) Z Y Magnetic Field
Radar backscatter is that portion of scattered waves returning in the direction of the sensor. Roughness of a surface depends on the interacting radar wavelength (a surface that behaves rough to a C band may be smooth to L band) Orientation of scatterers (vertical or horizontal) determine whether HH or VV polarization will dominate
Washington DC Radar Image
Relief displacement on
Radar Applications Sea ice monitoring (icebergs) Geology (faults, drainage patterns, topography) Floods, tides Glacier monitoring Crop boundaries and soil moisture Forest structure and biomass Ocean waves and currents Land/water contrast Coastal surveillance (erosion)
NASA Shuttle Radar Terrain Mission (SRTM) - Feb 2000 Objective: to generate high resolution global DEM coverage
Contrasting SRTM DEM(30m) and existing global DEM (1km)
Forest Species Composition and Structure Research using NASA s AIRSAR (Multiband/Multipolarized RADAR flown in Lear Jet) The pine plantations and bottomland hardwood forest - Southern Mississippi. *See Publication (PERS) & handout (summary) April 14, 2015
AIRSAR image of NASA s J.C. Stennis Space Center, Mississippi NASA - Stennis Space Center, MS Diffuse- hardwood Specular Corner reflectors Diffuse - pine This image is an L- band multipolarization composite using RGB- VV,HH,HV. AIRSAR L band (23 cm wavelength) Black areas are mostly specular surfaces such as grass and roads, white (corner reflectors) are buildings and structures, light blue are pine and pinehardwood (right side), and mostly floodplain, bottomland hardwood (browns) on left side.
AIRSAR L-band, HV Polarization- Forest Biomass Relationship Linear increase in HV backscatter signal with Pine biomass only up to approx. 100 tons/acre above-ground green weight biomass Poor relationship of HV, L band RADAR with uneven age bottomland hardwood forest biomass