Development and Application of Small Spaceborne Synthetic Aperture Radars (1998) / Chapter Skim
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2 SAR Issues
2 SAR Issues
Pages 12-27
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From page 12... ...
In part because of technological limitations, these studies concentrated on the amplitude of the radar backscatter and did not investigate phase information. Many current studies use SAR imagery to confirm these earlier results and extend them in the spatial domain.
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From page 13... ...
Interferometry Interferometric SAR is a technology that uses the phase difference between two coherent synthetic aperture radar images of a scene, obtained by two receivers separated by a cross-track distance called the baseline, to measure the height of the imaged surface. The ~nterferometric technique was first applied to SAR by Graham (1974)
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From page 14... ...
In the repeat pass approach two spatially close radar observations of the same scene are made at two different times. The time interval may range from minutes to years.
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From page 15... ...
All of these considerations, as well as their relationships to transmitter power requirements, spatial resolution, swath width, onto size and weight, and data rate were factored in Be final design com~ig~tion of the Shuttle Radar Topography Mission (SRTM) , planned for flight in September 1999.
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From page 16... ...
applications require ground resolution finer than a few tens of meters. The increasing cost of higher power and greater weight to obtain a very fine resolution, in the judgment of the committee, does not appear to be justified for most mission foci.
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From page 17... ...
Requirements Ecology Biomass, regrowth, cover- Lead + Chad 25-50 3 months None lope classification + P~uad Vegetation moisture Lead + Chad 25-50 10-15 days None + Piqued Vegetation height and L |
From page 18... ...
Ship Davigationinseaice C-HH + L-HH 50 2-3 days Wide swath + X-~ Coastalwetlands C-HH + X-HH 25-50 10 days NOTE: L-, C-, P-, X, Microwave wavelengths or bands used in radar signals; quad, quad-polari~tion, uses all four combinations of emitting and receiving polanzabons; copol, copolarization; interf, interferome~y; dual, dual pola~on; HH, horizontally polarized emitting and receiving signals; NED, noise equivalent (measure of radar b~kscatter or radar cross section) ; dB, decibels.
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From page 19... ...
Targeted coverage Long time series, regular repeats Local coverage, high resolution Regional and local coverage Long time series; regular repeats; L band L-band repeat-pass interferometry within 8 days, or C-band within 2 days, at latitude >65° Repeat-pass interferometry (1-2 days) or pattern matching L-band repeat-pass interferometry within 8 days, or C-band within 2 days L-band HV L-band HV or P-band HV P-band HV L-band dual polarization L-band quad polarization L-band HV 19 Validated (line of sight)
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From page 20... ...
Transmitter costs may increase with a short wavelength, but probably not as much as antenna costs decrease. This is partly due to a requirement for more power at short wavelengths, but the fact that scattering coefficients are larger at shorter wavelengths can mitigate this to some extent.
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From page 21... ...
In this connection, it has been shown that range and az~nuth resolution may be traded, as Interpretability for a given number of looks depends on the area of a pixel, not on its dimension In either direction (Moore, 1979~. However, swath width and the need to obtain more looks may make fine range resolution necessary, even though this increases the power required as well as the cost of transmitterspacecraft power.
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From page 22... ...
Use of the spotlight mode precludes continuous coverage and requires scanrung the beam In a horizontal direction. The cost trade-offs Implied by these alternatives must be explored if an application requ~r~g fine resolution is the mission focus.
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From page 23... ...
, the less desirable it is to fuse multifrequency data acquired at different tunes from multiple sensing platforms. Examples include phenomena such as the moisture status of soil and vegetation, which can change over a matter of seconds in windy conditions.
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From page 24... ...
Reliable orthorectification techniques have recently been demonstrated for a number of spaceborne SAR systems, but they require good (i.e., vertical postings < 30 m) digital elevation models (DEMs)
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From page 25... ...
The multipolar~zation data expected from Envisat and PALSAR lead to moderate cIassi~cation accuracies that are slightly inferior to those from multifrequency composites. The expected classification accuracy of the L-band polar~metric LightSAR baseline design is somewhat better than that obtained from ERS-IERS fusion and significantly better than that from ERS-1 and 2, JERS-l, or Radarsat ~one.
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From page 26... ...
1 - 1 I~,~,~_t~l at . FIGURE 2.2 Land cover cIassification performance of SAR design options.
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From page 27... ...
The LightSAR business development and system design definition studies submitted to NASA In November 1997 may help accomplish this for some commercial applications. Industry teams can be expected to pay close attention to the end-to-send costs of any system enhancements relative to the expected commercial value of such a system.
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