Determination of Primary Spectral Bands for Remote Sensing of Aquatic Environments.

Zhongping Lee,Robert Arnone,Kendall Carder,Mingxia He

doi:10.3390/s7123428

Abstract

About 30 years ago, NASA launched the first ocean-color observing satellite:the Coastal Zone Color Scanner. CZCS had 5 bands in the visible-infrared domain with anobjective to detect changes of phytoplankton (measured by concentration of chlorophyll) inthe oceans. Twenty years later, for the same objective but with advanced technology, theSea-viewing Wide Field-of-view Sensor (SeaWiFS, 7 bands), the Moderate-ResolutionImaging Spectrometer (MODIS, 8 bands), and the Medium Resolution ImagingSpectrometer (MERIS, 12 bands) were launched. The selection of the number of bands andtheir positions was based on experimental and theoretical results achieved before thedesign of these satellite sensors. Recently, Lee and Carder (2002) demonstrated that foradequate derivation of major properties (phytoplankton biomass, colored dissolved organicmatter, suspended sediments, and bottom properties) in both oceanic and coastalenvironments from observation of water color, it is better for a sensor to have ~15 bands inthe 400 - 800 nm range. In that study, however, it did not provide detailed analysesregarding the spectral locations of the 15 bands. Here, from nearly 400 hyperspectral (~ 3-nm resolution) measurements of remote-sensing reflectance (a measure of water color)taken in both coastal and oceanic waters covering both optically deep and optically shallowwaters, first- and second-order derivatives were calculated after interpolating themeasurements to 1-nm resolution. From these derivatives, the frequency of zero values foreach wavelength was accounted for, and the distribution spectrum of such frequencies wasobtained. Furthermore, the wavelengths that have the highest appearance of zeros wereidentified. Because these spectral locations indicate extrema (a local maximum orminimum) of the reflectance spectrum or inflections of the spectral curvature, placing the bands of a sensor at these wavelengths maximizes the potential of capturing (and then restoring) the spectral curve, and thus maximizes the potential of accurately deriving properties of the water column and/or bottom of various aquatic environments with a multi-band sensor.

Highlights

Since the successful demonstration of the Coastal Zone Color Scanner (CZCS) in measuring the spatial and temporal variation of phytoplankton via observation of ocean color (Gordon et al 1983; Gordon and Morel 1983), the importance of observing ocean and coastal waters with sensors in the visible domain is getting more and more attention from various countries
In this study, based on extensive and inclusive measurements of hyperspectral remote-sensing reflectance curves from various aquatic environments, the primary bands that optimally capture the spectral signatures of Rrs are determined via first- and second-order derivatives
These bands in general cover the operational bands of Seaviewing Wide Field-of-view Sensor (SeaWiFS), Moderate-Resolution Imaging Spectrometer (MODIS) and MERIS, and provide important and useful suggestions and guidance for extra bands of future multi-band sensors, in order to provide more and improved results for remote sensing of oceanic and coastal waters

Summary

Introduction

Since the successful demonstration of the Coastal Zone Color Scanner (CZCS) in measuring the spatial and temporal variation of phytoplankton via observation of ocean color (Gordon et al 1983; Gordon and Morel 1983), the importance of observing ocean and coastal waters with sensors in the visible domain is getting more and more attention from various countries. Lee and Carder (2002) demonstrated that for adequate remote sensing of major properties (water column and bottom) of both open ocean and complex coastal aquatic environments, a sensor requires ~ 15 spectral bands in the 400 – 800 nm range in order to obtain similar results as a sensor with 81 consecutive bands with 5-nm spacing. It is not yet clear, where the 15 bands should be placed. # OF MEASUREMENTS [CHL] RANGE (MG/M3) 0.07 – 49.0 0.06 – 0.5 0.3 – 0.9 1.7 – 20.7

Data and Methods

Results and Discussions

Summary