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Clark, D. K.

Publications and source records attributed to Clark, D. K..

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Ocean Optics Protocols for Satellite Ocean Color Sensor Validation

This document stipulates protocols for measuring bio-optical and radiometric data for the SIMBIOS Project. It supersedes the earlier version, and is organized into four parts: Introductory Background, Instrument Characteristics, Field Measurements and Data Analysis, Data Reporting and Archival. Changes in this revision include the addition of three new chapters: (1) Fundamental Definitions, Relationships and Conventions; (2) MOBY, A Radiometric Buoy for Performance Monitoring and Vicarious Calibration of Satellite Ocean Color Sensors: Measurement and Data Analysis Protocols; and (3) Normalized Water-Leaving Radiance and Remote Sensing Reflectance: Bidirectional Reflectance and Other Factors. Although the present document represents another significant, incremental improvement in the ocean optics protocols, there are several protocols that have either been overtaken by recent technological progress, or have been otherwise identified as inadequate. Revision 4 is scheduled for completion sometime in 2003. This technical report is not meant as a substitute for scientific literature. Instead, it will provide a ready and responsive vehicle for the multitude of technical reports issued by an operational Project. The contributions are published as submitted, after only minor editing to correct obvious grammatical or clerical errors.

Mueller, James L.↗
NASA NTRS2002

Ocean Optics Protocols for Satellite Ocean Color Sensor Validation

This document stipulates protocols for measuring bio-optical and radiometric data for the SIMBIOS Project. It supersedes the earlier version, and is organized into four parts: Introductory Background, Instrument Characteristics, Field Measurements and Data Analysis, Data Reporting and Archival. Changes in this revision include the addition of three new chapters: (1) Fundamental Definitions, Relationships and Conventions; (2) MOBY, A Radiometric Buoy for Performance Monitoring and Vicarious Calibration of Satellite Ocean Color Sensors: Measurement and Data Analysis Protocols; and (3) Normalized Water-Leaving Radiance and Remote Sensing Reflectance: Bidirectional Reflectance and Other Factors. Although the present document represents another significant, incremental improvement in the ocean optics protocols, there are several protocols that have either been overtaken by recent technological progress, or have been otherwise identified as inadequate. Revision 4 is scheduled for completion sometime in 2003. This technical report is not meant as a substitute for scientific literature. Instead, it will provide a ready and responsive vehicle for the multitude of technical reports issued by an operational Project. The contributions are published as submitted, after only minor editing to correct obvious grammatical or clerical errors.

Mueller, James L.↗
NASA NTRS1985

Ocean color measurements

Ocean color observations by the Coastal Zone color scanner (CZCS) aboard the Nimbus-7 satellite are discussed, together with the factors contributing to the 'apparent' color of the ocean. The CZCS optical systems and the tecniques for extraction of the phytoplankton pigment concentration and the diffuse attenuation coefficient K from the 'apparent' water color are described in detail. Special consideration is given to the use of biooptical algorithms and the development of the K algorithm for the CZCS imagery. It is shown that under typical atmospheric conditions, the pigment concentration can be extracted from the satellite imagery to within + or - 30 percent over concentration ranges from 0 to 5 mg/cu m for the Morel case 1 water (Morel and Prieur, 1977), to which the oceanic waters belong as a rule.

Gordon, H. R.↗
NASA NTRS1983

Nimbus 7 CZCS - Reduction of its radiometric sensitivity with time

Preliminary results are described for an effort to quantify the sensitivity decay of a radiometry sensor (the Coastal Zone Color Scanner or CZCS aboard Nimbus 7). The method used in the study is to (1) compute the water-leaving radiance for imagery acquired in regions where this radiance is known or can be independently estimated, and (2) adjust the sensor calibration to force agreement between the two radiances. Decay factors for orbit numbers from 0 to 20,000 are plotted, and surface and space measurements are compared for the Gulf Stream and the Northern Sargasso Sea at different seasons. The fact that a seasonal variability in the chlorophyll a concentration in the Sargasso Sea was found in the sensor analysis (apparently the first such satellite observation) increases confidence in the method.

Gordon, H. R.↗
NASA NTRS1983

Phytoplankton pigment concentrations in the Middle Atlantic Bight - Comparison of ship determinations and CZCS estimates

The processing algorithms used for relating the apparent color of the ocean observed with the Coastal-Zone Color Scanner on Nimbus-7 to the concentration of phytoplankton pigments (principally the pigment responsible for photosynthesis, chlorophyll-a) are developed and discussed in detail. These algorithms are applied to the shelf and slope waters of the Middle Atlantic Bight and also to Sargasso Sea waters. In all, four images are examined, and the resulting pigment concentrations are compared to continuous measurements made along ship tracks. The results suggest that over the 0.08-1.5 mg/cu m range, the error in the retrieved pigment concentration is of the order of 30-40% for a variety of atmospheric turbidities. In three direct comparisons between ship-measured and satellite-retrieved values of the water-leaving radiance, the atmospheric correction algorithm retrieved the water-leaving radiance with an average error of about 10%. This atmospheric correction algorithm does not require any surface measurements for its application.

Gordon, H. R.↗
NASA NTRS1981

Clear water radiances for atmospheric correction of coastal zone color scanner imagery

The possibility of computing the inherent sea surface radiance for regions of clear water from coastal zone color scanner (CZCS) imagery given only a knowledge of the local solar zenith angle is examined. The inherent sea surface radiance is related to the upwelling and downwelling irradiances just beneath the sea surface, and an expression is obtained for a normalized inherent sea surface radiance which is nearly independent of solar zenith angle for low phytoplankton pigment concentrations. An analysis of a data base consisting of vertical profiles of upwelled spectral radiance and pigment concentration, which was used in the development of the CZCS program, confirms the virtual constancy of the normalized inherent sea surface radiance at wavelengths of 520 and 550 nm for cases when the pigment concentration is less than 0.25 mg/cu m. A strategy is then developed for using the normalized inherent sea surface radiance in the atmospheric correction of CZCS imagery.

Gordon, H. R.↗
NASA NTRS1980

Nimbus-7 coastal zone color scanner - System description and initial imagery

Initial imagery from the Nimbus-7 Coastal Zone Color Scanner (CZCS) shows subtle variations in water color. Organisms, especially phytoplankton, play a major influence on the variations in water color. Processing of the visual data is described, and in particular, the use of an algorithm to remove aerosol from the image is discussed. Data on the six spectral bands (433-12,500 nm) are presented and comparisons are made between the CZCS and the Landsat-1 multispectral scanner. The implications for management of fisheries is noted.

Hovis, W. A.↗
NASA NTRS1980

Phytoplankton pigments from the Nimbus-7 Coastal Zone Color Scanner - Comparisons with surface measurements

Algorithms are developed for removing aerosol effects in visual data from the Nimbus-7 Coastal Zone Color Scanner (CZCS). The corrected imagery reveals eddy-like ocean circulation patterns. Pigment concentrations from CZCS are compared with surface determinations. CZCS imagery estimates pigment concentration to within 0.5 log C, where C is the sum of the concentrations of chlorophyll a and phaeopigments a

Gordon, H. R.↗
NASA NTRS1980

Upwelled spectral radiance distribution in relation to particulate matter in sea water

Spectral analysis of water color and concurrent measurements of the relative concentration of various particulate and dissolved constituents within a broad range of water types are necessary to quantify ocean color observations and successfully relate them to various biological and physical processes that can be monitored by remote sensing. Some of the results of a Nimbus-G prelaunch cruise in connection with the Coastal Zone Color Scanner (CZCS) experiment, which was carried out in the Gulf of Mexico in October 1977, are presented and discussed. Based upon a small but diverse sample of near-surface measurements, it appears possible to estimate total suspended particulate matter (SPM) to useful accuracies by forming ratios of the spectral radiances measured at wavelengths falling near the centers of certain CZCS bands, viz., 440 nm:550 nm and 440 nm:520 nm. Furthermore, the analysis suggests a very high degree of covariation between SPM and phytoplankton pigments except for certain well-defined special cases.

Clark, D. K.↗
NASA NTRS1980

Atmospheric effects in the remote sensing of phytoplankton pigments

The accuracy with which relevant atmospheric parameters must be estimated to derive photoplankton pigment concentrations of a given accuracy, from measurements of the ocean's apparent spectral radiance at satellite altitudes, is examined. A phytoplankton pigment algorithm is developed which relates the pigment concentration (c) to the three ratios of upwelling radiance just beneath the sea surface which can be formed from wavelengths (lambda) 440, 520 and 550 nm.

Gordon, H. R.↗
NASA NTRS1980

Initial coastal zone color scanner imagery

The characteristics of the Nimbus-7 Coastal Zone Color Scanner are presented and the atmospheric correction and bio-optical algorithms are reviewed. Comparison of imagery before and after atmospheric correction shows that water features such as color fronts and small scale eddies can be retrieved even through a hazy and horizontally inhomogeneous atmosphere. Imagery is also presented to show that features revealed in color are sometimes completely absent from simultaneous thermal imagery implying that color and thermal imagery can provide complementary rather than redundant information.

Gordon, H. R.↗
NASA NTRS1974

Computer derived coastal water classifications via spectral signatures

In April 1973, the National Environmental Satellite Service conducted a remote sensing investigation within the coastal waters of the New York Bight. Remote sensor records acquired from the ERTS-1 Multispectral Scanner and the Bendix 24 Channel Multispectral Scanner records flown on the NASA C-130 were used for water mass classification. Computer-derived classifications are discussed and compared. Such features as the Hudson River's turbid discharge plumes, acid waste and shelf water are examined in terms of their distribution of suspended particulates (2-203 microns), transmissivity, diffuse attenuation, incident and returned spectral irradiances. The characteristics of these features and their relationship to the computer derived classifications are presented and discussed with respect to radiative transfer theory.

Clark, D. K.↗
NASA NTRS1972

A study of temporal estaurine flow dynamics

Multispectral photography,infrared imagery, image enhancement, and oceanographic, radiometric, and meteorological data were used in the study of temporal estuarine flow dynamics, nearshore circulation, and the resulting dispersal of suspended and dissolved substances introduced from the continent. Repetitive multispectral photography, IR imagery, total radiance and irradiance, water surface temperatures, salinity, total suspended solids, visibility, current velocity, winds, dye implants, and high contrast image enhancement were used to observe and describe water mass boundaries in the nearshore zone and to attempt to establish on what repetitive scale these coastal features should be observed to better understand their behavior. Water mass variability patterns, seen naturally and with the use of dyes, along the North Carolina coast and in the Chesapeake Bay are being studied as synoptic data on the basic dynamics of circulation, flushing, and mixing in coastal waters.

Mairs, R. L.↗