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

Deriving inherent optical properties from water color: a multiband quasi-analytical algorithm for optically deep waters

For open ocean and coastal waters, a multiband quasi-analytical algorithm is developed to retrieve absorption and backscattering coefficients, as well as absorption coefficients of phytoplankton pigments and gelbstoff. This algorithm is based on remote-sensing reflectance models derived from the radiative transfer equation, and values of total absorption and backscattering coefficients are analytically calculated from values of remote-sensing reflectance. In the calculation of total absorption coefficient, no spectral models for pigment and gelbstoff absorption coefficients are used. Actually those absorption coefficients are spectrally decomposed from the derived total absorption coefficient in a separate calculation. The algorithm is easy to understand and simple to implement. It can be applied to data from past and current satellite sensors, as well as to data from hyperspectral sensors. There are only limited empirical relationships involved in the algorithm, and they are for less important properties, which implies that the concept and details of the algorithm could be applied to many data for oceanic observations. The algorithm is applied to simulated data and field data, both non-case1, to test its performance, and the results are quite promising. More independent tests with field-measured data are desired to validate and improve this algorithm.

Oceanic radiance model development and validation: application of airborne active-passive ocean color spectral measurements

It is shown that airborne active-passive (laser-solar) ocean color data can be used to develop and validate oceanic radiance models. The two principal inputs to the oceanic radiance model, chlorophyll pigment and incident solar irradiance, are obtained from a nadir-viewing laser-induced fluorescence spectrometer and a zenith-viewing radiometer, respectively. The computed water-leaving radiances are validated by comparison with the calibrated output of a separate nadir-viewing radiometer subsystem. In the North Atlantic Ocean, the calculated and the observed airborne radiances are found to compare very favorably for the 443-, 520-, and 550-nm wavelengths over an ∼ 170-km flight track east of St. John's, Newfoundland. The results further suggest that the semianalytical radiance model of ocean color, the airborne active (laser) fluorescence spectrometer, and the passive (solar) radiometric instrumentation are all remarkably precise.

Asymmetrical spectral curvature algorithms: oceanic-constituents sensitivities

The asymmetrical spectral curvature algorithm for Morel case 1 waters has been characterized by application of the semianalytical radiance model of ocean color to post-Coastal Zone Color Scanner (CZCS) sensor bands. Results of the study suggest that the [L (490)/L (443)][L (490)/L (555)] asymmetrical spectral curvature algorithm has a higher pigment-retrieval sensitivity than does the [L (490)/L (443)][L (490)/L (510)] curvature algorithm that was initially identified for pigment recovery. When this [L (490)/L (443)][L (490)/L (555)] algorithm was highlighted for study, it was found to (a) xhibit pigment-retrieval sensitivity that is intermediate to the [L (443)/L (555)] and the [L (510)/L (555)] CZCS-type radiance-ratio algorithms, (b) have less sensitivity to nonabsorbing particulate backscatter (NAB) than the [L (443)/L (555)] radiance ratio, (c) display remarkable insensitivity to the absorption of dissolved organic material (DOM), and (d) possess a NAB invariance point at an algorithm value of ∼1.8 (corresponding to a pigment concentration of ∼0.35 mg/M(3)). At this invariance point the [L (490)/L (443)][L (490)/L (555)] algorithm is insensitive to a wide concentration range of coccolith-like backscatterers in addition to being insensitive to DOM. The dual DOM and NAB insensitivity of the algorithm at a specific curvature value and chlorophyllous-pigment concentration suggests that such invariance points should be further studied for possible use in (1) the validation of other chlorophyllouspigment algorithms or model inversions and (2) the computation of other inherent optical properties.

Detection of phytoplankton pigments from ocean color: improved algorithms

Passive ocean-color data at 32 wavelengths in the visible domain and laser-induced fluorescence line heights of chlorophyll and phycoerythrin, measured simultaneously from an aircraft in the New York Bight area, are used to examine the problem of developing algorithms for pigment retrieval from ocean-color data that would be capable of distinguishing between chlorophyll and phycoerythrin. Using factor analysis, it is shown that it is indeed possible to develop such algorithms. Furthermore, the wavelengths used in the algorithms can be reduced from 32 to 6 (similar to the SeaWiFS channels) without much loss in information. These multiwavelength algorithms yield significantly higher correlation coefficients for chlorophyll compared with the conventional blue-green ratio used for retrieval of this pigment. The Coastal Zone Color Scanner wavelengths appear to be inadequate for quantitative retrieval of the phycoerythrin signal.

Nondestructive measurement of chlorophyll pigment content in plant leaves from three-color reflectance and transmittance

We propose a nondestructive or optical method of measuring the chlorophyll content in a leaf after constructing a mathematical model of reflectance and transmittance of plant leaves as a function of their chlorophyll pigment content. The model is based on the Kubelka-Munk theory and involves the modeling of the multiple reflection of light in a leaf that is assumed to be composed of a stack of four layers. It also includes the assumption that the scattering coefficient and the absorption coefficient of the Kubelka-Munk theory can be expressed as a linear function of the pigment content of a plant leaf. In the proposed method, the chlorophyll content is calculated from reflectances and transmittances at three bands whose center wavelengths are 880,720, and 700 nm. Experiments were performed to confirm the applicability of the model and the method. Reflectance and transmittance calculated with the model showed good agreement with measured values. Furthermore, several unmeasurable constants necessary in the calculation were determined by a least-squares fit. We also confirmed that these results were consistent with several well-known facts in the botanical field. The method proposed here showed a small estimation error of 6.6 microg/cm (2) over the 0-80 microg/cm(2) chlorophyll content range for all kinds of plant tested.