Engineering topics

Brown, Gary S.

Publications and source records attributed to Brown, Gary S..

3 records

NASA NTRS1992

Issues related to waveform computations for radar altimeter applications

An algorithm has been developed to model the average return power waveforms available from general radar altimeter systems, such as the Multimode Airborne Radar Altimeter (MARA) system operated at NASA Goddard Space Flight Center - Wallops Flight Facility. The algorithm is based on a convolutional model comprised of three functions: the average flat surface impulse response (FSIR), the radar system point target response (PTR), and the height pdf of the specular points on the sea surface. The FSIR is modified to account for the asymmetric antenna beam used by the MARA system, and then certain properties of this modified SIR are exploited to obtain closed-form expressions that can be rapidly evaluated. An FFT convolution routine is used to further speed up the computations. The result is an algorithm that can be used to study the effects of pointing errors in surface measurements.

Newkirk, Michael H.↗

NASA NTRS1991

The science benefits of and the antenna requirements for microwave remote sensing from geostationary orbit

The primary objective of the Large Space Antenna (LSA) Science Panel was to evaluate the science benefits that can be realized with a 25-meter class antenna in a microwave/millimeter wave remote sensing system in geostationary orbit. The panel concluded that a 25-meter or larger antenna in geostationary orbit can serve significant passive remote sensing needs in the 10 to 60 GHz frequency range, including measurements of precipitation, water vapor, atmospheric temperature profile, ocean surface wind speed, oceanic cloud liquid water content, and snow cover. In addition, cloud base height, atmospheric wind profile, and ocean currents can potentially be measured using active sensors with the 25-meter antenna. Other environmental parameters, particularly those that do not require high temporal resolution, are better served by low Earth orbit based sensors.

Stutzman, Warren L.↗

NASA NTRS1989

A useful approximation for the flat surface impulse response

The flat surface impulse response (FSIR) is a very useful quantity in computing the mean return power for near-nadir-oriented short-pulse radar altimeters. However, for very small antenna beamwidths and relatively large pointing angles, previous analytical descriptions become very difficult to compute accurately. An asymptotic approximation is developed to overcome these computational problems. Since accuracy is of key importance, a condition is developed under which this solution is within 2 percent of the exact answer. The asymptotic solution is shown to be in functional agreement with a conventional clutter power result and gives a 1.25-dB correction to this formula to account properly for the antenna-pattern variation over the illuminated area.

Brown, Gary S.↗