Engineering Papers⌕ Search

Engineering topics

Roy, N. A.

Publications and source records attributed to Roy, N. A..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The wind-speed measurement capability of spaceborne radar altimeters

This study represents an attempt to quantitatively assess the capability of a spaceborne radar altimeter to infer ocean surface wind speeds from a measurement of the backscattered power at vertical incidence. The study uses data acquired during 184 near overflights of NOAA data buoys with the GEOS-3 satellite radar altimeter and encompasses a wind-speed range from less than 1 to 18 m/s. An algorithm is derived from the data comparison for converting measurements of the normalized scattering cross section of the ocean surface at 13.9 GHz into estimates of the surface wind speed at the standard anemometer height of 10 m. The algorithm is straightforward and potentially useful for on-board processing of raw altimeter data for the purpose of providing real-time estimates of surface wind speed. For winds in the range of 1 to 18 m/s, the mean difference between the altimeter-inferred winds and the buoy measurements is negligible while the standard deviation of the difference is 1.74 m/s.

Brown, G. S.↗
NASA NTRS1972

Error model for the SAO 1969 standard earth.

A method is developed for estimating an error model for geopotential coefficients using satellite tracking data. A single station's apparent timing error for each pass is attributed to geopotential errors. The root sum of the residuals for each station also depends on the geopotential errors, and these are used to select an error model. The model chosen is 1/4 of the difference between the SAO M1 and the APL 3.5 geopotential.

Martin, C. F.↗
NASA NTRS1972

Rapid global geoid mapping with satellite altimetry.

Theoretical demonstration of the feasibility to build, fly, calibrate, and evaluate an orbiting altimeter system that is to offer the basis for accurate geoidal mapping on a global scale. The problems involved in instrumentation and orbit determination are discussed. Following a description of the Skylab altimeter characteristics, a more advanced design is postulated. This new design is shown to be capable of an accuracy of better than 50 cm and noise levels of 20 cm. With proper premission analysis and careful scheduling, a global geoidal map of 1- to 2-meter resolution can be obtained within an 18- to 20-day period by using a high-inclination orbit.

Stanley, H. R.↗
NASA NTRS1971

An error analysis of the recovery capability of the relative sea-surface profile over the Puerto Rican trench from multi-station and ship tracking of GEOS-2

Error analyses were performed to examine the height error in a relative sea-surface profile as determined by a combination of land-based multistation C-band radars and optical lasers and one ship-based radar tracking the GEOS 2 satellite. It was shown that two relative profiles can be obtained: one using available south-to-north passes of the satellite and one using available north-to-south type passes. An analysis of multi-station tracking capability determined that only Antigua and Grand Turk radars are required to provide satisfactory orbits for south-to-north type satellite passes, while a combination of Merritt Island, Bermuda, and Wallops radars provide secondary orbits for north-to-south passes. Analysis of ship tracking capabilities shows that high elevation single pass range-only solutions are necessary to give only moderate sensitivity to systematic error effects.

Stanley, H. R.↗
NASA NTRS1970

Single arc tracking errors associated with altimeter measurements

This study investigated the accuracies of orbit determinations in the radial coordinate utilizing currently available tracking systems. The results pinpoint certain areas which are critical for the efficient utilization of altimeter measurements.

Mcgoogan, J. T.↗