Glossary and Acronyms

azimuth : The horizontal direction in radar sensing. In SAR, the along track direction

backscatter : Radar signal energy scattered back toward the instrument

BSA : Backscatter Alignment

carrier : The base frequency of the radar output which is modulated by the signal waveform

chirp : A linear FM waveform used for the outgoing radar pulse

clutter : Random background noise in a radar image due to scattering from a surface with homogeneous roughness on a scale larger than the signal wavelength

corner reflector : A trihedral target made from aluminum screen and oriented on the ground toward the radar to provide a bright pixel for image intensity calibration

DLR : Deutsches Zentrum für Luft- und Raumfahrt e. V. (German Aerospace Research Establishment)

EM waves : Electro Magnetic waves

FFT : Fast Fourier Transform. An efficient algorithm for computing the discrete Fourier transform of a discrete signal. Used in harmonic or spectral analysis

FM : Frequency Modulation, as of a carrier wave

footprint : The area on the ground intersected by the radar beam

frequency response function : The Fourier transform of the impulse response function

FSA : Forward Scattering Alignment

Geocoding : Geometric correction and registration of an image to map coordinates, often involving terrain correction for SAR images

GIS : Geo-Information System

global incidence angle : The angle of the radar beam center from the normal to the geoid surface at the target

GO : Geometrical Optics

ground range : The distance along the surface from the nadir point to the target

impulse response function : The characteristic function of a linear time-invariant filter, which, convolved with the input signal, produces the output

in-phase : Engineering term for the real part of a complex signal

linear frequency modulation : A phase coded pulse modulation of the carrier frequency

local incidence angle : The angle between the radar beam center and the normal to the local topography. The difference between the global incidence angle and the terrain slope

look : In SAR processing, an image processed with a fraction of the reference spectrum (chirp or Doppler) resulting in multiple images at reduced resolution

look angle : Of a SAR, the angle from the nadir at which the radar beam is pointed. Of a target, the angle between the SAR-nadir and SAR-target lines

matched filter : A filter designed to compress a known signal into a short pulse. Equivalent to pulse compression by cross-correlation with the time reversed conjugate of the expected waveform

nadir track : The path on the surface directly below the flight path of the instrument

PO : Physical Optics

Polarisation : The orientation of the electromagnetic field vector of the transmitted radar signal

quadrature : Engineering term for the imaginary part of a complex signal

range : The distance direction for a radar. In SAR, the cross track direction

resolution : The ability of the radar and processing system to discriminate between targets on the ground

SAR : Synthetic Aperture Radar

slant range : The distance from radar to target

SLC : Single Look Complex, ERS-1 SAR Product

SNR : Signal to Noise Ratio

speckle : Spatially random multiplicative noise due to coherent superposition of multiple backscatter sources within a SAR resolution element

squint angle : The angle between the radar beam center and the normal to the flight path

swath : The strip of ground swept over by the moving radar beam

TEM waves: Transversal Electro Magnetic waves

terrain slope : The angle between the local tangent to the surface and the horizontal

window : A finite duration weighting function, commonly of unit energy, which is multiplied against a signal for the purpose of improving the spectrum by removing high frequency components due to truncation in time