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At least 1,225 records · Page 68
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NASA NTRS1986

Active-passive airborne ocean color measurement. I - Instrumentation

The instrumentation used in a multichannel lidar fluorosensor spectrometer functioning concurrently as a passive spectroradiometer for measuring upwelling ocean color radiance is discussed. The instrument calibration techniques are addressed, including the absolute passive calibration technique, the importance of relative channel-to-channel calibration for accurate ocean color measurement, and active mode calibration techniques using passive calibration transfer methods. Ground and flight test results from the dual-mode active-passive ocean color sensor are discussed.

Hoge, F. E.↗
NASA NTRS1986

Active-passive airborne ocean color measurement. II - Applications

Reported here for the first time is the use of a single airborne instrument to make concurrent measurements of oceanic chlorophyll concentration by (1) laser-induced fluorescence, (2) passive upwelling radiance, and (3) solar-induced chlorophyll fluorescence. Results from field experiments conducted with the NASA airborne oceanographic lidar (AOL) in the New York Bight demonstrate the capability of a single active-passive instrument to perform new and potentially important ocean color studies related to (1) active lidar validation of passive ocean color in-water algorithms, (2) chlorophyll a in vivo fluorescence yield variability, (3) calibration of active multichannel lidar systems, (4) effect of sea state on passive and active ocean color measurements, (5) laser/solar-induced chlorophyll fluorescence investigations, and (6) subsequent improvement of satellite-borne ocean color scanners. For validation and comparison purposes a separate passive ocean color sensor was also flown along with the new active-passive sensor during these initial field trials.

Hoge, F. E.↗
NASA NTRS1985

Observations of the polar regions from satellites using active and passive microwave techniques

Observations of the ocean ice, ice sheets, ice edges, and ocean waves in the Antarctic, performed by the Seasat and Nimbus-7 satellites are described. Specific features of the Seasat altimeter, the SAR, the Seasat-A Scatterometer System, and the Scanning Multichannel Microwave Radiometer (SMMR) are discussed, together with the advantages and limitations of each instrument as applied to the study of ice dynamics. The Nimbus-7 SMMR algorithm for calculating sea-ice concentrations is presented. In addition, the Seasat altimeter-derived data on wind speed and wave heights in the Southern Ocean, and on the ice sheets of the Antarctica and Greenland were evaluated.

Swift, C. T.↗
NASA NTRS1985

Electronically Steered Thinned Array Radiometer (ESTAR) system design, calibration, and sensitivity

The ESTAR system, an imaging L-band radiometer designed to provide measurements of soil moisture from space, is described. The large aperture size dictated by the resolution requirement (10 km or less) suggests the use of aperture synthesis, and plans to have ESTAR operate in low earth orbit require that the synthesis be performed in the short data acquisition time permitted by satellite motion. Two forms of ESTAR are described. ESTAR-0 is to be an airborne prototype designed for proof of concept; it will image a line of eight adjacent pixels with 8 degree spatial resolution of 0.1 degree Kelvin temperature resolution, given 1 sec integration time. ESTAR-1 is the satellite version to operate from space. A tentative sensor design will image a line of 128 0.5 degree pixels with 2.0 degree K resolution assuming 0.7 sec integration at 700 km altitude.

Ruf, C.↗
NASA NTRS1985

Spectral measurements in support of SIR-B using the Surface Contour Radar

The use of the Surface Contour Radar (SCR) from an aircraft to obtain spectral information on the seas off the tip of South America, in support of the SIR-B experiment in October 1984, is reported. The SCR is a computer-controlled 36-GHz radar that measures sea surface directional wave spectra and produces a real-time topographical map of the surface below the aircraft. Ground tracks and polar plots of the data obtained are illustrated.

Walsh, E. J.↗
NASA NTRS1985

Elimination of directional wave spectrum contamination from noise in elevation measurements

The Surface Contour Radar (SCR) is a 36-GHz computer-controlled airborne radar which generates a false-color-coded elevation map of the sea surface below the aircraft in real time, and can routinely produce ocean directional wave spectra with post-flight data processing which have much higher angular resolution than pitch-and-roll buoys. The SCR range measurements are not error-free and the resulting errors in the elevations corrupt the directional wave spectrum. This paper presents a technique for eliminating that contamination.

Walsh, E. J.↗
NASA NTRS1986

The Electronically Steered Thinned Array Radiometer (ESTAR)

The concept of a thinned array radiometer is described as an alternate to large filled apertures to achieve high resolution imaging from space. The serious limitations of conventional mechanical scanning systems and the practical problems associated with a multiple receiver pushbroom system that utilizes a large antenna are discussed. The thinned array is developed in terms of aperture synthesis techniques used in radio astronomy. Examples of thinned array configurations are presented, and future directions are discussed.

Swift, C. T.↗
NASA NTRS1987

NASA sea ice and snow validation plan for the Defense Meteorological Satellite Program special sensor microwave/imager

This document addresses the task of developing and executing a plan for validating the algorithm used for initial processing of sea ice data from the Special Sensor Microwave/Imager (SSMI). The document outlines a plan for monitoring the performance of the SSMI, for validating the derived sea ice parameters, and for providing quality data products before distribution to the research community. Because of recent advances in the application of passive microwave remote sensing to snow cover on land, the validation of snow algorithms is also addressed.

Cavalieri, Donald J.↗
NASA NTRS1986

Active-passive correlation spectroscopy - A new technique for identifying ocean color algorithm spectral regions

A new active-passive airborne data correlation technique has been developed which allows the validation of existing in-water oceoan color algorithms and the rapid search, identification, and evaluation of new sensor band locations and algorithm wavelength intervals. Thus far, applied only in conjunction with the spectral curvature algorithm (SCA), the active-passive correlation spectroscopy (APCS) technique shows that (1) the usual 490-nm (center-band) chlorophyll SCA could satisfactorily be placed anywhere within the nominal 460-510-nm interval, and (2) two other spectral regions, 645-660 and 680-695 nm, show considerable promise for chlorophyll pigment measurement. Additionally, the APCS method reveals potentially useful wavelength regions (at 600 and about 670 nm) of very low chlorophyll-in-water spectral curvature into which accessory pigment algorithms for phycoerythrin might be carefully positioned. In combination, the APCS and SCA methods strongly suggest that significant information content resides within the seemingly featureless ocean color spectrum.

Hoge, F. E.↗
NASA NTRS1986

Chlorophyll pigment concentration using spectral curvature algorithms - An evaluation of present and proposed satellite ocean color sensor bands

During the past several years symmetric three-band (460-, 490-, 520-nm) spectral curvature algorithm (SCA) has demonstrated rather accurate determination of chlorophyll pigment concentration using low-altitude airborne ocean color data. It is shown herein that the in-water asymmetric SCA, when applied to certain recently proposed OCI (NOAA-K and SPOT-3) and OCM (ERS-1) satellite ocean color bands, can adequately recover chlorophyll-like pigments. These airborne findings suggest that the proposed new ocean color sensor bands are in general satisfactorily, but not necessarily optimally, positioned to allow space evaluation of the SCA using high-precision atmospherically corrected satellite radiances. The pigment concentration recovery is not as good when existing Coastal Zone Color Scanner bands are used in the SCA. The in-water asymmetric SCA chlorophyll pigment recovery evaluations were performed using (1) airborne laser-induced chlorophyll fluorescence and (2) concurrent passive upwelled radiances. Data from a separate ocean color sensor aboard the aircraft were further used to validate the findings.

Hoge, Frank E.↗
NASA NTRS1987

Circumstances for Pluto-Charon mutual events in 1987

Circumstances are tabulated for 88 Pluto-Charon mutual events occurring during the 1987 opposition. Charon is predicted to be completely obscured either by Pluto or Pluto's shadow during each passage behind Pluto during this opposition, providing several opportunities to study Pluto uncontaminated by the light of Charon. The duration of these total events is predicted to be from 32 to 79 min. The mutual-event season is now expected to conclude during the 1990 opposition. Two new stars have been selected as comparison stars for events occurring prior to opposition in 1987. Standardization of the primary comparison stars used in 1985 and 1986 has yielded the following magnitudes: B = 12.6044 + or - 0.0015 and V = 11.7956 + or - 0.0017 (1985 Primary); B = 13.1238 + or 0.0008 and V = 12.3885 + or - 0.0014 (1986 Primary).

Tholen, David J.↗
NASA NTRS1987

Ocean color spectral variability studies using solar-induced chlorophyll fluorescence

It is suggested that chlorophyll-induced ocean color spectral variability can be studied using only a passive airborne spectroradiometer instrument, with solar-induced chlorophyll fluorescence used as the standard against which all correlations are performed. The intraspectral correlation (ISC) method is demonstrated with results obtained during an airborne mapping mission in the New York Bight. The curvature algorithm is applied to the solar-induced chlorophyll fluorescence at about 690 nm, and good agreement is found with results obtained using active-passive correlation spectroscopy. The ISC method has application to spectral variability and resulting chlorophyll concentration measurement in different environmental conditions and in different water types.

Hoge, Frank E.↗
NASA NTRS1987

Wave-measurement capabilities of the surface contour radar and the airborne oceanographic lidar

The 36-gigahertz surface contour radar and the airborne oceanographic lidar were used in the SIR-B underflight mission off the coast of Chile in October 1984. The two systems and some of their wave-measurement capabilities are described. The surface contour radar can determine the directional wave spectrum and eliminate the 180-degree ambiguity in wave propagation direction that is inherent in some other techniques such as stereophotography and the radar ocean wave spectrometer. The Airborne Oceanographic Lidar can acquire profile data on the waves and produce a spectrum that is close to the nondirectional ocean-wave spectrum for ground tracks parallel to the wave propagation direction.

Walsh, Edward J.↗
NASA NTRS1987

Radiance-ratio algorithm wavelengths for remote oceanic chlorophyll determination

Two-band radiance-ratio in-water algorithms in the visible spectrum have been evaluated for remote oceanic chlorophyll determination. Airborne active-passive (laser-solar) data from coastal, shelf-slope, and blue-water regions were used to generate two-dimensional chlorophyll-fluorescence and radiance-ratio statistical correlation matrices containing all possible two-band ratio combinations from the thirty-two available contiguous 11.25-nm passive bands. The principal finding was that closely spaced radiance-ratio bands yield chlorophyll estimates which are highly correlated with laser-induced chlorophyll fluorescence within several distinct regions of the ocean color spectrum. Band combinations in the yellow, orange-red, spectral regions showed considerable promise for satisfactory chlorophyll pigment estimation in near-coastal Case II waters. Pigment recovery in Case I waters was best accomplished using blue-green radiance ratios in the 490/500-nm region.

Hoge, Frank E.↗
NASA NTRS1987

A microwave radiometer weather-correcting sea ice algorithm

A new algorithm for estimating the proportions of the multiyear and first-year sea ice types under variable atmospheric and sea surface conditions is presented, which uses all six channels of the SMMR. The algorithm is specifically tuned to derive sea ice parameters while accepting error in the auxiliary parameters of surface temperature, ocean surface wind speed, atmospheric water vapor, and cloud liquid water content. Not only does the algorithm naturally correct for changes in these weather conditions, but it retrieves sea ice parameters to the extent that gross errors in atmospheric conditions propagate only small errors into the sea ice retrievals. A preliminary evaluation indicates that the weather-correcting algorithm provides a better data product than the 'UMass-AES' algorithm, whose quality has been cross checked with independent surface observations. The algorithm performs best when the sea ice concentration is less than 20 percent.

Walters, J. M.↗
NASA NTRS1987

A multifrequency microwave radiometer of the future

The design of the High-Resolution Multifrequency Microwave Radiometer (HMMR), which is to be installed on EOS, is described. The HMMR is to consist of the Advanced Microwave Sounding Unit (AMSU), the Advanced Mechanically Scanned Radiometer (AMSR), and the Electronically Scanned Thinned Array Radiometer (ESTAR). The AMSU is a 20-channel microwave radiometer system designed to measure profiles of atmospheric temperature and humidity and the AMSR is a microwave imager with channels at 6, 10, 18, 21, 37, and 90 GHz for measuring snow cover over land, the age and areal extent of sea ice, the intensity of precipitation over oceans and land, and the amount of water in the atmosphere. ESTAR is an imaging radiometer operating near 1.4 GHz capable of obtaining global maps of surface soil moisture with a spatial resolution of about 10 km. The antenna and signal processing utilized in the ESTAR to achieve the real aperture resolution are examined.

Le Vine, D.↗
NASA NTRS1987

Observations of and a new model for fetch-limited wave growth

The Surface Contour Radar (SCR) is a 36-GHz computer-controlled airborne radar which generates a false-color coded elevation map of the sea surface below the aircraft in real time. In the present paper, SCR observations are discussed which demonstrate the existence of a full developed sea state. These observations are used to judge the validity of growth rates for fetch-limited wave spectrum development and lead to new refinements in the modeling of wave generation by wind. It is noted that the observations have resolved an apparent paradox in the JONSWAP and Donelan et al. (1985) fetch-limited algorithms.

Walsh, E. J.↗
NASA NTRS1985

Airborne lidar experiments at the Savannah River Plant

The results of remote sensing experiments at the Department of Energy (DOE) Savannah River Nuclear Facility utilizing the NASA Airborne Oceanographic Lidar (AOL) are presented. The flights were conducted in support of the numerous environmental monitoring requirements associated with the operation of the facility and for the purpose of furthering research and development of airborne lidar technology. Areas of application include airborne laser topographic mapping, hydrologic studies using fluorescent tracer dye, timber volume estimation, baseline characterization of wetlands, and aquatic chlorophyll and photopigment measurements. Conclusions relative to the usability of airborne lidar technology for the DOE for each of these remote sensing applications are discussed.

Krabill, William B.↗