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Madsen, S. N.

Publications and source records attributed to Madsen, S. N..

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Fine Resolution Topographic Mapping of the Jovian Moons: A Ka-Band High Resolution Topographic Mapping Interferometric Synthetic Aperture Radar

The topographic data set obtained by MOLA has provided an unprecedented level of information about Mars' geologic features. The proposed flight of JIMO provides an opportunity to accomplish a similar mapping of and comparable scientific discovery for the Jovian moons through use of an interferometric imaging radar analogous to the Shuttle radar that recently generated a new topographic map of Earth. A Ka-band single pass across-track synthetic aperture radar (SAR) interferometer can provide very high resolution surface elevation maps. The concept would use two antennas mounted at the ends of a deployable boom (similar to the Shuttle Radar Topographic Mapper) extended orthogonal to the direction of flight. Assuming an orbit altitude of approximately 100km and a ground velocity of approximately 1.5 km/sec, horizontal resolutions at the 10 meter level and vertical resolutions at the sub-meter level are possible.

Madsen, S. N.↗
NASA NTRS2003

Decimeter-Wavelength Polarimetric Radar Imaging of the Icy Moons of Jupiter

Imaging radars with wavelengths in the range of 10 cm to 1 m can deeply penetrate the surface of an icy body, revealing details of the geomorphology, local structure, and electrical properties of the upper layers. Radar studies of icy surfaces on Earth have used the polarization state of backscatter echoes at multiple frequencies to characterize the surface and subsurface properties of glaciers, showing relatively smooth surfaces on the scale of radar wave-lengths, and subsurface scattering from volume scatterers consistent with ice pipes and lenses. These volume scattering effects are evident in enhanced polarization ratios over a limited range of backscatter incidence angles. The Galilean satellites exhibit similarly enhanced polarization ratios and volumetric scattering effects, but the observations are limited in angular resolution, leading to ambiguity in interpreting the scattering mechanisms and their structural implications.

Rosen, P. A.↗
NASA NTRS2002

Understanding and responding to earthquake hazards

Advances in understanding of the earthquake cycle and in assessing earthquake hazards is a topic of great importance. Dynamic earthquake hazard assessments resolved for a range of spatial scales and time scales will allow a more systematic approach to prioritizing the retrofitting of vulnerable structures, relocating populations at risk, protecting lifelines, preparing for disasters, and educating the public.

earth science vision distributed spacecraft virtua↗
NASA NTRS1998

Synthetic Aperture Radar Interferometry

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 characteristics of the surface. This paper reviews the techniques of interferometry, systems and limitations, and applications in a rapidly growing area of science and engineering.

remote sensing SAR Synthetic Aperture Radar interf↗
NASA NTRS1994

Results of 1993 Repeat-Pass SAR Interferometry Experiments

In this talk we present results of a repeat-pass SAR interferometry experiment performed in June 1993 near Portage, Maine. Differential GPS data accurate to +/-10cm were acquired to aid in motion compensation and geolocation of targets in the imagery. The experiment and data analysis will be discussed, and results will be shown during the presentation.

SAR interferometry repeat-pass AIRSAR↗
NASA NTRS1992

Real-time processor for the Danish airborne SAR

A real-time processor for the Danish high-resolution SAR is presented in terms of its functional performance, algorithm, architecture, and implementation. The real-time processor is mainly intended to assist the operator in using the SAR system, but since the processor has been designed to produce high-quality images, it is expected to make off-line processing superfluous in many cases. The range-Doppler algorithm is adopted and supplemented with an extensive motion compensation, considering the special conditions related to the real-time strip mapping of large scenes. The processor is a pipeline of about 20 elements interconnected by a dedicated data path and a control bus. Only three different types of elements are involved: a programmable signal processing element, a multipurpose memory element, and a multipurpose interface element. The prototypes of these three elements have been tested with satisfactory results.

Dall, J.↗
NASA NTRS1991

Development of a calibration workstation for SIR-C

The paper describes the status of a comprehensive synthetic aperture radar (SAR) software package developed specifically to aid the calibration of a multifrequency and multipolarization radar like the Shuttle Imaging Radar, SIR-C. The primary data types processed are engineering telemetry, point targets (corner reflectors and polarimetric active radar calibrators), distributed targets (clutter), tone-generators, and ground receivers. The parameters derived to aid the calibration of the production processor include measurements of relative radiometric channel to channel imbalance, absolute calibration constants, antenna pattern corrections, noise levels, polarimetric cross-talk, and geometric offsets. The software reports standard performance measurements such as resolution, peak and integrated sidelobes, radiometric response accuracy, and geometrical distortions such as scale errors, position bias and standard deviation, and image skew. Furthermore, the inclusion of software to allow updates of the shuttle-state vector (position and velocity) is considered.

Madsen, S. N.↗
NASA NTRS1991

Improved geometric calibration of the SIR-C data

Errors in the determination of the platform state vector (position and velocity) limit the accuracy with which individual pixels in a SAR (synthetic aperture radar) image can be located. A method of updating the state vector based on the SAR data is described. The algorithm combines reference targets at known locations with the estimates available from the mission control center, utilizing a maximum likelihood estimator. The targets can be located at calibration sites or be easily recognizable targets of opportunity. The accuracy of the update depends on the number of targets, their geometry, and the accuracy of their position determination. The algorithm is tested using Seasat SAR data. High-accuracy state vectors were perturbed by Gaussian distributed errors with standard deviations and cross-correlations based on worst-case expectations for SIR-C (Shuttle Imaging Radar). Tests using ground targets located in topographic maps (1:24,000) showed that state vector position errors on the order of 300-400 m and velocity accuracies of 2-3 m/s are readily achievable.

Madsen, S. N.↗