[1] The Shuttle Radar Topography Mission produced the most complete, highest-resolution digital elevation model of the Earth. The project was a joint endeavor of NASA, the National Geospatial-Intelligence Agency, and the German and Italian Space Agencies and flew in February 2000. It used dual radar antennas to acquire interferometric radar data, processed to digital topographic data at 1 arc sec resolution. Details of the development, flight operations, data processing, and products are provided for users of this revolutionary data set.

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The Shuttle Radar Topography Mission

Temporal and geometrical decorrelation often prevents SAR interferometry from being an operational tool for surface deformation monitoring and topographic profile reconstruction. Moreover, atmospheric disturbances can strongly compromise the accuracy of the results. The authors present a complete procedure for the identification and exploitation of stable natural reflectors or permanent scatterers (PSs) starting from long temporal series of interferometric SAR images. When, as it often happens, the dimension of the PS is smaller than the resolution cell, the coherence is good even for interferograms with baselines larger than the decorrelation one, and all the available images of the ESA ERS data set can be successfully exploited. On these pixels, submeter DEM accuracy and millimetric terrain motion detection can be achieved, since atmospheric phase screen (APS) contributions can be estimated and removed. Examples are then shown of small motion measurements, DEM refinement, and APS estimation and removal in the case of a sliding area in Ancona, Italy. ERS data have been used.

Permanent scatterers in SAR interferometry

We present a new differential synthetic aperture radar (SAR) interferometry algorithm for monitoring the temporal evolution of surface deformations. The presented technique is based on an appropriate combination of differential interferograms produced by data pairs characterized by a small orbital separation (baseline) in order to limit the spatial decorrelation phenomena. The application of the singular value decomposition method allows us to easily "link" independent SAR acquisition datasets, separated by large baselines, thus increasing the observation temporal sampling rate. The availability of both spatial and temporal information in the processed data is used to identify and filter out atmospheric phase artifacts. We present results obtained on the data acquired from 1992 to 2000 by the European Remote Sensing satellites and relative to the Campi Flegrei caldera and to the city of Naples, Italy, that demonstrate the capability of the proposed approach to follow the dynamics of the detected deformations.

/pdf/a-new-algorithm-for-surface-deformation-monitoring-based-on-ot8ep5chnm.pdf

A new algorithm for surface deformation monitoring based on small baseline differential SAR interferograms

On February 22, 2000 Space Shuttle Endeavour landed at Kennedy Space Center, completing the highly successful 11-day flight of the Shuttle Radar Topography Mission (SRTM). Onboard were over 300 high-density tapes containing data for the highest resolution, most complete digital topographic map of Earth ever made. SRTM is a cooperative project between NASA and the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense. The mission was designed to use a single-pass radar interferometer to produce a digital elevation model (DEM) of the Earth's land surface between about 60 deg north and 56 deg south latitude. When completed, the DEM will have 30 m pixel spacing and about 15 m vertical accuracy. Two orthorectified image mosaics (one from the ascending passes with illumination from the southeast and one from descending passes with illumination from the southwest) will also be produced.

Synthetic aperture radar interferometry is an imaging technique for measuring the topography of a surface, its changes over time, and other changes in the detailed characteristic of the surface. By exploiting the phase of the coherent radar signal, interferometry has transformed radar remote sensing from a largely interpretive science to a quantitative tool, with applications in cartography, geodesy, land cover characterization, and natural hazards. This paper reviews the techniques of interferometry, systems and limitations, and applications in a rapidly growing area of science and engineering.

/pdf/synthetic-aperture-radar-interferometry-28lm7jf0if.pdf

Synthetic aperture radar interferometry

A radar brightness map of Venus has been obtain d. It reveals interesting surface features and much structure over a large area.

http://science.sciencemag.org/content/sci/169/3949/974.full.pdf

A radar snapshot of venus.

A new type of spectrometer for space application has been developed and tested in the laboratory which measures separately, mass/charge and the three‐dimensional velocity distribution of incident ions. The instrument has relatively high resolution (m/Δm = 600 amu/m) and allows rapid measurement of the four‐dimensional set: mass/charge, speed, elevation angle, and azimuth angle. The basic components include: (1) a sector magnet which serves as a momentum/charge filter with a very wide angular acceptance, (2) an electrostatic deflector which spreads the momentum‐analyzed ion beam according to energy/charge (or mass/charge), (3) microchannel plate detectors with position sensitive readout, and (4) a set of grids with variable applied voltage to accelerate or decelerate the incident ions before they enter the analysis part of the instrument. For application in a comet environment an electrostatic mirror would be used to reflect ions into the instrument while preventing dust from entering the field of view.

Energetic ion mass spectrometer

Two Mass/Charge (M/Q) of about 2 distributions were observed by the Giotto Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) during the encounter with comet Halley. The first, present throughout the encounter, is identified as solar wind He(2+). The second, detectable only within about 600,000 km of the nucleus, is identified as H2(+) (produced primarily by dissociation and ionization of cometary H2O). When these two distributions are separated, distinct differences in their dynamics are apparent, particularly in the density and velocity profiles near the 'cometopause'.

Cometary H2+ and solar wind He2+ dynamics across the Halley cometopause

The feasibility of studying Venus by radar was demonstrated on the tenth of March, 1961, when an echo from Venus was first detected in real time.

The spectrum of the echo may be expected to be broadened by the doppler shifts produced by any rotation Venus might have. In order to measure this broadening, a novel technique for accurate spectral estimation of this extremely weak signal was devised, analyzed and implemented. The results of the measurements indicate that Venus rotates only once for each of its years, so that one hemisphere always faces the sun. In addition, the spectral measurements together with some polarization measurements enable one to infer some scattering properties of the surface.

Time of flight measurements were also made, using a cross-correlation technique. These, compared with standard astronomical tables, provide a new value for the Astronomical Unit. The standard deviation of these measurements is only a few parts in 10^7.

Radar exploration of Venus

Radar observations of Icarus were made in mid-June 1968, at the time of closest approach. From the data, it is estimated that the radius is between 0.3 and 0.6 kilometer and the rotation period between 1.5 and 3.3 hours. A set of round-trip Doppler shift measurements is given.

Richard M. Goldstein

Papers

A radar snapshot of venus.

Energetic ion mass spectrometer

Cometary H2+ and solar wind He2+ dynamics across the Halley cometopause

Radar exploration of Venus

Radar observations of icarus.