Roswell W. Austin

Nimbus-7 Coastal Zone Color Scanner: System Description and Initial Imagery

The Coastal Zone Color Scanner (CZCS) on Nimbus-7, launched in October 1978, is the only sensor in orbit that is specifically designed to study living marine resources. The initial imagery confirms that CZCS data can be processed to a level that reveals subtle variations in the concentration of phytoplankton pigments. This development has potential applications for the study of large-scale patchiness in phytoplankton distributions, the evolution of spring blooms, water mass boundaries, and mesoscale circulation patterns.

Gulf of Mexico, ocean-color surface-truth measurements

In October 1977, a major remote sensing experiment was conducted in the Gulf of Mexico, in preparation for the launch of NIMBUS-7 which carried the Coastal Zone Color Scanner. Two major vessels obtained surface-truth measurements, while two jet aircraft at altitudes of 12.5 and 19.5 km obtained images of the surrounding ocean in 10 spectral bands. Measurements obtained in the surface water from the NOAA vessel Researcher of the spectral downwelling irradiances, upwelling radiances, attenuation and scattering properties are described.

Coastal Zone Color Scanner Radiometry

The characteristics of the Coastal Zone Color Scanner (CZCS) are described. The factors affecting the apparent radiance signature at the satellite are presented along with some representative examples of measured spectral radinces, irradiances and transmittances in the ocean and in the atmosphere. Finally an example is presented of the spectral radiance components measured and computed for an experiment conducted in southern California coastal waters for the purpose of obtaining surface validation data at the time of a satellite overpass.

Ocean color measurements

Publisher Summary This chapter focuses on ocean color measurements. The techniques for the extraction of the phytoplankton pigment concentration and the diffuse attenuation coefficient ( K ) of the water, from the coastal zone color scanner (CZCS) observations of the “apparent” color of the ocean, are described in detail. It is shown that under typical atmospheric conditions the pigment concentration can be extracted from the satellite imagery to within about ±30% over concentration ranges from 0 to 5 mg m –3 for Morel case 1 water. For case 1 water, the simultaneous measurement of K provides an indication of the depth in the water (l/ K ) over which the CZCS “weighs” the pigment concentration. A detailed overview of the CZCS system is also presented. Response to oceanic and atmospheric conditions is analyzed. Development of the bio-optical algorithm for remote sensing of the phytoplankton pigment concentration is elaborated, and application of the bio-optical algorithms to CZCS imagery is described. Remote sensing of the diffuse attenuation coefficient of water is also discussed in this chapter.

Spectral dependence of the diffuse attenuation coefficient of light in ocean waters: a reexamination using new data

A model devised earlier1,2 relating the spectral dependence of K(.), the attenuation coefficient for natural diffuse light in the ocean, to the value of K()) at a reference wavelength, is re-examined using recently acquired data. The original model was based on data obtained from 1 967 to 1 979 by various investigators using a variety of scanning submersible spectroradiometers in tropical to mid-latitude waters. New data were obtained by the Visibility Laboratory in a series of cruises from 1985 to 1987 covering ocean latitudes from 24.4° to 77.4°. These data are believed to be of uniformly high quality and have the advantage over the previous data in that they permit the determination of K()) profiles to 200 meters from data obtained simultaneously at all 12 wavelengths and over a time span of approximately 6 minutes, vice data recorded serially at each wavelength and at discrete depths over a time span of as much as one to two hours with the spectroradiometers. An examination of the variation in the spectral K(A)s with latitude was prompted by a concern that the phytoplankton species distribution at high latitudes might differ sufficiently from that at tropical to mid-latitudes to require a change in the spectral K(.) model. A comparison was also performed between 83 sets of spectral K(A)s derived from the new data and K(X)s predicted by the model using measured K(490) as an input index. Small systematic differences were found which are not believed to be significant for most applications, hence, no change in the model is recommended on the basis of these findings.

Underwater laser scanning system

A system is described that produces high quality images through turbid waters by means of time encoded reflected light transmitted by scattering. The system consists of a compact battery operated laser scanning unit that scans the underwater scene with the laser beam in a manner similar to a television raster. Light reflected from any object in the scene varies in accordance with the reflectance of the minute spot being illuminated. This time varying intensity (TVI) signal is transmitted through the water to a remote receiver by both scattered and unscattered light where the received signal may be stored and/or displayed. The underwater laser scanning unit can be moved freely about the field of interest by scuba diver or ROV, unencumbered by entangling umbilicals, and can send real-time images over distances of 15 to 20 attenuation lengths to observers in a shirt-sleeve environment for critical viewing on an image display monitor. This previously undescribed system was developed in the early 1970s for proof of concept tests and used technology that is now 18 or more years old. The physical principles and the experimental hardware are described and examples are given of images providing exquisite detail that were made in an experimental tank together with some images obtained in ocean trials.

Ultraviolet Submersible Spectroradiometer

An increase in the incidence of solar ultraviolet radiation upon oceans and lakes, as a consequence of anthropogenic diminishing of the ozone in the stratosphere, might well have a significant effect upon primary producers and other aquatic organisms in these waters. Existing data were inadequate for accurately estimating the penetration of biologically effective dosages of present and potential future levels of UV irradiance into various natural waters. An underwater spectroradiometer, designed specifically to measure spectral irradiance in the middle ultraviolet (MUV, 280-340 nm), has been designed, constructed and used to obtain ecologically important data.

An Oceanographic Illuminometer System For Light Penetration And Reflection Studies

An improved illuminometer system is described which consists of a dual underwater illuminometer and a deck illuminometer both having improved light collecting properties and a new deck measurement unit. The instrument can provide direct measurements of (1) the illumination on the ocean surface, (2) the ratio of the downwelling illumination in the ocean to that on the ocean surface, (3) the ratio of the upwelling to the downwelling illumination in the ocean, (4) diffuse attenuation coefficient, K, for the downwelling light field, and (5) the depth of the underwater sensor. Emphasis in the design of the equipment has been to provide a system with which the operator can quickly obtain direct, accurate settings and to minimize the opportunity for human error in reading the results. The design philosophy of the lambertian light collector and the photoelectric circuitry is given along with the resulting performance. Examples of the data obtained with this system and its applications are given.

Remote Sensing Of Ocean Color

The development of multispectral scanners flown on aircraft and satellites have led to the use of these for measuring ocean color remotely. Potentially, this remote sensing of color will substantially increase the oceanographers ability to monitor chlorophyll and particulate concentration in the upper layers over large spatial areas. Research conducted over the past several years has developed the techniques and laid the ground work for the quantitative interpretation of the remote sensed signals. It has been shown the meaningful corrections to these signals for atmospheric scattering can be made and that the resultant inherent signal can be correlated with in-situ measurements of chlorophyll and particulate matter concentration. A review of these experiments and techniques is presented.

Volume-Scattering Functions in Ocean Waters

Absolute values of the volume-scattering function, obtained in situ for a variety of natural ocean waters, are presented. The use of optical techniques to infer the concentration, optical characteristics, and size distribution of suspended particulate material in the ocean is outlined. The technique of using single-angle scatter meters to estimate the total volume-scattering function (and hence the suspended particle concentration) is discussed and an optimization of the technique, based upon the data presented, is suggested.