Engineering topics

Mcintosh, Robert E.

Publications and source records attributed to Mcintosh, Robert E..

6 records

NASA NTRS1995

Investigation of microwave backscatter from the air-sea interface

Monitoring the ocean surface winds and mean ocean surface level is essential for improving our knowledge of the climate. Two instruments that may provide us with this information are satellite-based scatterometers and altimeters. However, these instruments measure the backscatter characteristics of the ocean surface from which other physical parameters, such as the wind speed or ocean surface height, are derived. To improve the algorithms or models that relate the electromagnetic backscatter to the desired physical parameters, the University of Massachusetts (UMass) Microwave Remote Sensing Laboratory (MIRSL) designed and fabricated three airborne scatterometers: a C-band scatterometer (CSCAT), Ku-band scatterometer (KUSCAT) and C/Ku-band scatterometer (EMBR). One or more of these instruments participated in the Electromagnetic Bias experiment (EM Bias), Shelf Edge Exchange Processes experiment (SEEP), Surface Wave Dynamics Experiment (SWADE), Southern Ocean Wave Experiment (SOWEX), Hurricane Tina research flights, Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE), and Ladir In-space Technology Experiment (LITE). This document describes the three scatterometers, summarizes our measurement campaigns and major contributions to the scientific and engineering communities, lists the publications that resulted, and presents the degrees earned under the support of this NASA grant.

Mcintosh, Robert E.↗

NASA NTRS1993

A stepped-frequency Delta-K microwave radar for oceanographic studies

A stepped-frequency Delta-K (SFDK) radar was developed to remotely sense ocean surface characteristics. This C-band radar uses frequency diversity and real-time signal processing for improved Delta-K measurements. In this paper, we show how frequency diversity can be implemented to enhance the energy of the resonant peak of the cross-product spectrum relative to the background energy. This feature is essential for making real-time measurements of resonant peak frequency over extended time periods. The SFDK was used in a month-long field experiment at N. Truro (Massachusetts). The results presented show that the phase velocity of ocean surface waves could be precisely measured 87 percent of the time.

Popstefanija, Ivan↗

NASA NTRS1993

Electromagnetic bias in sea surface range measurements at frequencies of the TOPEX/POSEIDON satellite

Measurements of EM bias at the 13.6 GHz and 5.3 GHz operating frequencies of the NASA altimeter on the TOPEX/POSEIDON satellite in a series of 11 aircraft flights from January 17, 1991 through March 4, 1991, during the Surface Wave Dynamics Experiment, are reported. The data are consistent with an earlier set of airborne measurements and indicate that EM bias is slightly higher at 5.3 GHz than at 13.6 GHz, and that the magnitudes of both biases increase with increasing wind speed, as does their difference. With some exceptions, EM bias shows little variation over a mesoscale region on a given day or within 1 or 2 h, but it can change significantly over a 6-h period. Recent tower, airborne, and satellite measurements exhibit a consistency in the characteristics of the wind speed dependence but suggest that there may be a height dependence in the determinations, with the bias decreasing with increasing altitude.

Hevizi, Laszlo G.↗

NASA NTRS1992

Measurements of the effects of surface winds on ocean currents with a stepped-frequency Alpha K radar system

A frequency-agile C band Alpha K radar system was used to measure ocean surface currents during the SAXON-Chesapeake Light Tower experiment. Surface currents were measured with the radar approximately 80 percent of the time from September 20 to October 14, 1988. These measurements are compared with in situ current and wind probe measurements. The agreement between the radar and current probe measurements are found to be very good during periods when the wind- and wave-driven currents are negligible in the radar-viewing direction. During other times, the radar measurements are approximated by the Weber model.

Popstefanija, Ivan↗

NASA NTRS1991

A C-band scatterometer for remote sensing the air-sea interface

An airborne C-band scatterometer system (C-Scat) has been developed to remotely sense ocean surface winds and improve upon the present understanding of the relationship between normalized radar cross section (NRCS) and ocean surface roughness influences such as wind speed and direction, wave height and slope, and the air-sea temperature difference. The scatterometer utilizes a unique frequency-steered microstrip array antenna that is installed beneath the fuselage of an airplane. The antenna is electronically scanned in elevation, from 20 deg to 50 deg off-nadir, and mechanically spins in azimuth. The system is capable of measuring ocean surface NRCS from altitudes as high as 25,000 ft. The transmitter and receiver operate from 4.98 to 5.7 GHz. System parameters such as transmitter pulse width, pulse repetition frequency, output power level, and receiver bandwidth are programmable. Received signals can be averaged and displayed in real time and are stored on a Winchester disk drive for post-flight analysis. Preliminary flight data that demonstrates the instrument's performance is presented.

Mclaughlin, David J.↗

NASA NTRS1989

Microwave measurements of ocean currents for the SAXON experiment

Measurements of ocean surface currents carried out during the SAXON experiment using the University of Massachusetts stepped-frequency Delta-K radar (SFDKR) are presented. The measurement site was the Chesapeake light tower situated in the north Atlantic Ocean, 15 km off the coast of Virginia Beach, Virginia. The radar was placed on a platform 26 m above mean sea level. Measurements were made at grazing angles between 3 and 10 deg. A nearly uninterrupted record of ocean current velocity was obtained for a 26-day period. The measurement dependence on various system and hydrodynamic parameters and a comparison with an independent in-situ current measurement (EM current meter) are presented. Experimental results show that the Delta K spectrum with a distinguishable resonant line can be measured under all weather conditions, from calm seas with large swells to the fully developed seas occurring under winds as high as 20 ms-1. The only parameter that needs to be adjusted in real time is the frequency separation, Delta f, which has to be modified according to the varying shape of the ocean wave spectrum. Currents could not be accurately measured for very low wind conditions, even though resonant lines were present in the Delta K spectrum. The SFDKR can accurately measure wind-driven surface currents for wide range of wind conditions.

Popstefanija, Ivan↗