Coastal Zone Color Scanner Data Research Articles

Simulated effects of barometric pressure and ozone content upon the estimate of marine phytoplankton from space

Barometric pressure and total ozone content may significantly depart from their mean climatology values; these values, however, are used when processing the visible remote sensing (VRS) data with the aim of estimating the phytoplanktonic pigments concentration (chlorophyll a + phaeophytin a, in milligrams per cubic meter) within the upper ocean. The effect of ignoring such departures upon the retrieved concentration has been simulated for the broad oceanic range (0.015–20 mg/m3). The simulation is effected for typical VRS situations (geometry, aerosol) when information about the variable aerosol is not available when entering the processing (as is the case with the Coastal Zone Color Scanner (CZCS) data) or, conversely, when such information has been separately obtained (simulation of future sensors with dedicated near‐IR channels). The result is that in both these cases the use of mean climatology values leads to variable misestimates of the pigment content, by a factor of up to 2 in many common VRS situations, and above 2 for very low or high actual pigment content. After the results are discussed, the conclusion is that the actual values of the barometric pressure and of the ozone content will have to be introduced in the processing of future visible sensor data in order to preserve the expected accuracy. With regard to the exploitation of the CZCS archive, this requirement is not so essential, insofar as the pressure and ozone effects on the pigment concentration retrieval remain of the same order as the noise due to the limited radiometric accuracy of this sensor. However, at the scale of a CZCS scene, neglecting the strong structures in the pressure and ozone content fields may bias the phytoplankton concentration mapping. The use of the actual values is therefore recommended.

The North Sea: Satellite colour atlas

Satellite imagery of the North Sea from the Coastal Zone Color Scanner (CZCS) shows complex seasonal changes in the optical and biological properties of surface waters, features which have not been resolved, hitherto, through direct observations from ships. Selected scenes for the period 1979–1986, presented as single band (channel 3), colour composite (channels 1 + 2 + 3) and chlorophyll (channels 1/3 or 2/3) images, are used to demonstrate the relative surface distributions between February and October of suspended sediments, coccolithophores and plant pigments. Comparison are made also with sea surface temperature images from the Advanced Very High Resolution Radiometer (AVHRR). Quantitative evaluation of the CZCS data is restricted by a lack of contemporary in situ optical and biological measurements. However, chlorophyll and Secchi disc distributions, determined by measurements from research ships have been compared qualitatively with images from the Southern Bight (13 May 1986) and for the east central North Sea (24 August 1984 and 24 October 1985). Mini series of CZCS images are presented to show the annual coccolithophore blooms, the development of the spring bloom in the Skagerrak, June 1983 and summer chlorophyl distributions in the German Bight.

An algorithm for estimating the water quality parameters from irradiance just below the sea surface

An algorithm for estimating the water quality parameters such as chlorophyll concentration, backseattering coefficient of particles and absorption coefficient of yellow substance from the irradiance reflectance observed just below the sea surface is developed and discussed with a view to application in optical remote sensing. In this algorithm, an optical model technique is coupled with the fluorescence technique. The computed water quality parameters are compared with those observed directly from concurrent surface water samples. In this comparison, efforts have been made to minimize the number of spectral irradiance reflectances used in the computation while ensuring that computed water quality parameters fit well to the observed ones. The results show that the observed water quality parameters can be closely represented by those computed from at least four selected wavelengths: 480, 520, 600 and 685 nm. Further, it has been observed that a similar approach utilizing three coastal zone color scanner (CZCS) bands, 443, 520 and 620 nm, is applicable for interpretation of CZCS data.

Remote observations of the marine environment: Spatial heterogeneity of the mesoscale ocean color field in CZCS imagery of California near-coastal waters

Visible remote sensing provides synoptic observations of the ocean color field which illustrate the variability of optical properties in surface waters. This variability and its connections with phytoplankton patchiness in the marine environment are briefly examined. Quantitative assessments of ocean color were obtained from Coastal Zone Color Scanner data, by deriving large-scale, high-resolution images of the diffuse attenuation coefficient at 490 nm, for two regions off the California coast. Taking a statistical approach to the description of ocean surface characteristics (widely used in the literature for the analysis of chlorophyll concentration data, but rare for that of ocean color data), scalar power spectra of the diffuse attenuation coefficient variance have been estimated, for a number of subsets of the CZCS-derived images. No significant variations between the two regions considered appeared in the spectra, which all exhibit similar characteristics and an average power law dependency following approximately a - frsol|5/3 slope over the 10–100 km spectral window. The results obtained seem to compare favorably with other published examples of spectra derived from both shipboard and satellite measurements of surface parameters, and possibly to mirror the turbulent nature of the oceanic environment.

A two-look technique for studying atmospheric effects in optical scanner data for the ocean

Abstract The traditional method for validating calculated values of chlorophyll concentration in the sea is based on comparisons with in situ point measurements made from ships. In this paper we present an alternative approach based on a two-look method involving data from successive orbits of the NIMBUS-7 satellite. We present the results of some calculations based on the use of Coastal Zone Colour Scanner (CZCS) data for the Irish Sea viewed from two successive orbits of the NIMBUS-7 satellite. The method used involves a first attempt at a self-consistent approach to calculating the aerosol path radiance. Results are presented for two pairs of scenes from 6 April 1980 and 4 May 1980.

An algorithm for the retrieval of sediment content in turbid coastal waters from CZCS data

Abstract An algorithm for the retrieval of the sediment content of turbid coastal waters from Coastal Zone Colour Scanner (CZCS) data has been developed theoretically and tested against experimental values. The theoretical approach consisted of numerical simulations and sensitivity analyses, focused on the search for a retrieval variable with low sensitivity to chlorophyll-like pigments, and to uncertainties in the procedure for the determination of the atmospheric correction applied to the remotely measured radiances. The variableX, = [R(550) - R(670)]° [R{520)/R(550)]6where R(λ) is the subsurface irradiance reflectance at wavelength X, has been found to meet the above requirements, provided 0–5asλ 1·5 and – 2·5≤b≤–0·7. The algorithm log(sed.) = A + Blog(Ars) has been applied to the analysis of a set of CZCS scenes of the Adriatic Sea, with sediment and chlorophyll concentration ranges from 1 to 13gm-3 and from 0–1 to l–5mgm~3, respectively. The theoretically predicted low sensitivity to the atmospheric ...

Evaluation of sensitivity decay of Coastal Zone Colour Scanner (CZCS) detectors by comparison with in situ near-surface radiance measurements

Abstract Upwelling radiance and downwelling irradiance measurements were made at 0-65 nm intervals in the 400-700 nm spectral range from an aircraft flown at an altitude of 150m around 07.30, 10.06 and 11.07hours GMT. Each time the location was different and at each location the measurements were repeated three times. The NIMBUS-7 satellite overpass was at 10.04 hours GMT. The aerosol optical path length was evaluated from the in situ measured downwelling irradiance. The time dependence of the calibration slopes and intercepts of the Coastal Zone Colour Scanner (CZCS) was incorporated according to recent work by Gordon el at. The atmospheric contributions were removed from the measured radiances and from the CZCS data. The resulting water-leaving radiances were normalized so as to minimize those variations in the water-leaving radiance which arise from varying solar irradiance at the sea surface. A comparison between the normalized water-leaving radiance retrieved from airborne measurements (10.06 hours G...

Comparison between CZCS data from 10 July 1979 and simultaneous in situ measurements for south-eastern Scottish waters

Abstract This paper presents an analysis of coastal zone colour scanner (CZCS) data for a date for which simultaneous iin situ measurements exist. Using CZCS data of 10 July 1979 for the vicinity of Dundee, the inflight slope and intercept for all spectral bands were calculated. Comparison of these results with the pre-flight values show that the deviations of the inflight slopes from the pre-flight slopes for the visible bands are within 11 per cent, whereas the deviations in the intercepts are found to be rather larger. The contribution to the satellite-recorded radiance from the atmospheric interplay was removed using Sturm's atmospheric correction method which incorporates the iteration procedure described by Smith and Wilson. Many algorithms have been used for comparing the upwelling radiance with the in situ chlorophyll-like pigment concentrations. Although, some of the algorithms gave good correlation coefficients, the constants in the algorithms used turn out to be quite different from the values ...

Corrections for inflight calibration of the coastal zone colour scanner

Abstract The inflight calibration data of coastal zone colour scanner (CZCS) data for several scenes have been studied and it is shown that the calibration has changed with time. This variation cannot be neglected if one intends to extract quantitative information about suspended material in the sea from the CZCS data. This variation has been studied statistically and a set of correction formulae has been obtained for each of bands 1–4.

Delineation of seasonal changes of chlorophyll frontal boundaries in Mediterranean Coastal waters with Nimbus-7 Coastal Zone Color Scanner data

The seasonal changes in chlorophyll-like pigment distribution in the Northwestern Mediterranean Sea (Gulf of Lions) were monitored during the year 1979. Data were collected from the Coastal Zone Color Scanner (CZCS), carried on the Nimbus-7 satellite. A series of cloud-free images covering the whole year was selected and processed to evaluate chlorophyll-like pigment concentrations. The upwelling subsurface radiance of the ocean ( L ss) was extracted from the apparent upwelling signal reaching the satellite sensor ( L O) using an algorithm removing atmospheric effects. Chlorophyll-like pigment concentration ( C) was then derived from L ss in different wavelengths. Characteristic boundaries between water masses with different phytoplankton content were obtained. The results demonstrate that phytoplankton distribution is a good indicator of seasonal variations of oceanic fronts. Features such as coastal upwellings, cyclonic eddies, or plume of the Rhône river could be monitored.

Delineation of seasonal changes of chlorophyll frontal boundaries in Mediterranean coastal waters with Nimbus-7 Coastal Zone Color Scanner data

Delineation of seasonal changes of chlorophyll frontal boundaries in Mediterranean coastal waters with Nimbus-7 Coastal Zone Color Scanner data

Coastal zone colour scanner: failure of active calibration

The primary objective of the Coastal Zone Colour Scanner (CZCS) on board the Nimbus-7 satellite was to detect small variations in the water-leaving radiance because these variations in the water-leaving signal are caused by changes in the quality of the water. Using the in-flight calibration information from the housekeeping data for various dates, it is shown that the radiance from the calibration lamp is changing considerably with time. This changing radiance is shown to be consistent with a change in the temperature of the calibration lamp from its nominal value of 2000K. Thus there is a need to find a way to determine the correct value of the radiance from the calibration lamp. Unless the correct radiance is known, the in-flight calibration constants cannot be used to extract useful information from the CZCS data.

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.