Chapter 4
A TOOL FOR INVERSE MODELING OF SPECTRAL MEASUREMENTS
IN DEEP AND SHALLOW WATERS
PETER GEGE
1 AND ANDREAS ALBERT
2
1
DLR, Remote Sensing Technology Institute, P.O.Box 1116, 82230 Wessling, Germany
2
GSF, Institute of Soil Ecology, Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany
Email: peter.gege@dlr.de, andreas.albert@gsf.de
1. Introduction
Light is the primary energy source of life on Earth. Apart from some deep-sea
ecosystems, the existence of all organisms depends directly or indirectly on the process
of photosynthesis, which is driven by electromagnetic radiation in the spectral range
from 400 to 700 nm (photosynthetically active radiation, or PAR), or at longer
wavelengths for some photosynthetic bacteria. Solar irradiance and the transparency of
water are maximal, and atmospheric extinction is low, at PAR wavelengths. Thus,
optical measurements in this spectral range can provide valuable information to
characterize biological processes in aquatic ecosystems.
Many different types of optical instruments have been developed which can be
used to quantitatively determine certain parameters of aquatic ecosystems. These
instruments are operated on buoy, off shore platforms, ships, aircraft, and satellites, and
measure radiation in different spectral bands. Remote sensing instruments usually
provide images, thus measuring radiance spectra of individual pixels. In situ optical
instruments can measure radiation with angle-integration (irradiance), with
normalization to incident illumination (reflectance), with alterations versus depth
(attenuation), or the fractions which are absorbed, scattered, or emitted in the water or
from the dissolved or suspended constituents.
Usually data from each instrument, or sensor type, are analyzed with software that
is specifically tailored to that instrument or spectrum. However, operating a group of
programs is a potential source of errors, because the data analysis programs must be
consistent with each other with respect to the model formulations and input data. In
addition, maintenance and data handling are time consuming, as is training new staff.
For these reasons it is desirable to have a single integrative program. Such a tool, the
“Water colour Simulator” WASI, was developed for optical in situ measurements.
The
accompanying this book. It can also be downloaded from an ftp server (Gege, 2002a).
WASI is designed as a sensor-independent spectra generator and spectra analyzer.
The program has well documented calculation steps and automated, graphical
visualization of results. It can also generate and analyze large series of spectra. In the
forward mode, up to three parameters can be iterated simultaneously to produce a great
variety of spectra, while in the inverse mode an unlimited number of spectra can be
read from files and automatically analyzed. The supported spectrum types are listed in
Table 1. Calculations are based on analytical models. The data provided with WASI
were determined at Lake Constance (Gege, 1994, 1995; Heege, 2000), and are suited
for calculating all spectral types at a range of at least 390 to 800 nm and with 1 nm
spectral resolution.
program, together with a detailed user manual, is provided on the CD-ROM
81
and Management Applications, 81-109.
© 2006 Springer. Printed in the Netherlands.
L.L. Richardson and E.F. LeDrew (eds.), Remote Sensing of Aquatic Coastal Ecosystem Processes: Science
A TOOL FOR INVERSE MODELING OF SPECTRAL MEASUREMENTS
IN DEEP AND SHALLOW WATERS
PETER GEGE
1 AND ANDREAS ALBERT
2
1
DLR, Remote Sensing Technology Institute, P.O.Box 1116, 82230 Wessling, Germany
2
GSF, Institute of Soil Ecology, Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany
Email: peter.gege@dlr.de, andreas.albert@gsf.de
1. Introduction
Light is the primary energy source of life on Earth. Apart from some deep-sea
ecosystems, the existence of all organisms depends directly or indirectly on the process
of photosynthesis, which is driven by electromagnetic radiation in the spectral range
from 400 to 700 nm (photosynthetically active radiation, or PAR), or at longer
wavelengths for some photosynthetic bacteria. Solar irradiance and the transparency of
water are maximal, and atmospheric extinction is low, at PAR wavelengths. Thus,
optical measurements in this spectral range can provide valuable information to
characterize biological processes in aquatic ecosystems.
Many different types of optical instruments have been developed which can be
used to quantitatively determine certain parameters of aquatic ecosystems. These
instruments are operated on buoy, off shore platforms, ships, aircraft, and satellites, and
measure radiation in different spectral bands. Remote sensing instruments usually
provide images, thus measuring radiance spectra of individual pixels. In situ optical
instruments can measure radiation with angle-integration (irradiance), with
normalization to incident illumination (reflectance), with alterations versus depth
(attenuation), or the fractions which are absorbed, scattered, or emitted in the water or
from the dissolved or suspended constituents.
Usually data from each instrument, or sensor type, are analyzed with software that
is specifically tailored to that instrument or spectrum. However, operating a group of
programs is a potential source of errors, because the data analysis programs must be
consistent with each other with respect to the model formulations and input data. In
addition, maintenance and data handling are time consuming, as is training new staff.
For these reasons it is desirable to have a single integrative program. Such a tool, the
“Water colour Simulator” WASI, was developed for optical in situ measurements.
The
accompanying this book. It can also be downloaded from an ftp server (Gege, 2002a).
WASI is designed as a sensor-independent spectra generator and spectra analyzer.
The program has well documented calculation steps and automated, graphical
visualization of results. It can also generate and analyze large series of spectra. In the
forward mode, up to three parameters can be iterated simultaneously to produce a great
variety of spectra, while in the inverse mode an unlimited number of spectra can be
read from files and automatically analyzed. The supported spectrum types are listed in
Table 1. Calculations are based on analytical models. The data provided with WASI
were determined at Lake Constance (Gege, 1994, 1995; Heege, 2000), and are suited
for calculating all spectral types at a range of at least 390 to 800 nm and with 1 nm
spectral resolution.
program, together with a detailed user manual, is provided on the CD-ROM
81
and Management Applications, 81-109.
© 2006 Springer. Printed in the Netherlands.
L.L. Richardson and E.F. LeDrew (eds.), Remote Sensing of Aquatic Coastal Ecosystem Processes: Science