Geology Reference
In-Depth Information
The core information in this chapter addresses a few
concepts of remote sensing relevant to sea ice applications
and particularly its parameter retrieval. The presentation
focuses on the breadth rather than the depth of the infor-
mation in order to appeal to readers who want to develop
a quick acquaintance with scientific issues that are outside
their domain of experiences. This conforms to the overall
flavor of the topic—to work across disciplinary bounda-
ries in order to realize the promise of integrated informa-
tion. The reader will find a bias in the presentation in favor
of microwave remote sensing, although details of optical
and thermal infrared (TIR) sensing are also presented.
Space‐borne passive microwave observations have been
the most commonly used tool to monitor sea ice in the
polar region. Moreover, active microwave observations,
particularly from the synthetic aperture radar (SAR) sys-
tems, are the prime data source for mapping sea ice in
national centers of sea ice monitoring. In the microwave
section, more focus is placed on theoretical information
about SAR and its polarimtery technology. This includes
the mathematical formulations of the measured backscat-
ter, the decomposition and commonly used polarimetric
parameters, and the interpretation of the parameters in
terms of radar scattering mechanisms. This constitutes a
reasonable scientific summary that should benefit those
who plan to explore the value of radar observations
(including polarimetry) in sea ice applications.
The chapter starts by introducing basic definitions
and principles of satellite remote sensing in general
(section 7.1). This is followed by a section on historical
synopsis of satellite remote sensing for sea ice applica-
tions (section 7.2). An introduction to basic theoretical
concepts of electromagnetic (EM) wave and its propaga-
tion is included in section 7.3. Here, a few concepts are
briefly introduced with suggested references for readers
who are interested in more details. Two concepts are
covered in more detail: the brightness temperature of
emitted radiation and the polarization of the EM wave.
Sections 7.4, 7.5, and 7.6 present reviews on the three
categories of remote sensing: optical, thermal, and micro-
wave, respectively. In section 7.6.2, derivation of radar
equations, the concept of the backscatter coefficient, the
estimation of SAR spatial resolution, and most impor-
tantly the mathematical representation of SAR polarim-
teric data are presented. The latter is needed to support
the growing number of applications of this technology at
both scientific and operational levels. Remote sensing
observations of sea ice are affected by the presence of
three other media: atmosphere, seawater, and snow on ice.
Section 7.7 addresses basic information pertaining to the
EM propagation in these media. More weight in the dis-
cussions is given to the snow as it can modulate the
received signal from the underlying sea ice significantly,
especially when it metamorphoses into grains or develops
wetness.
7.1. General PrinciPles of satellite
remote sensinG
The three electromagnetic spectral regions used in EO
data applications, including sea ice, are optical, thermal
infrared (IR), and microwave. The spectral range of each
region and its divisions into subregions are shown in
Figure 7.1. However, the boundaries between these
regions or subregions are not unequivocally defined in
the literature. The optical region covers the three spectral
bands: the visible (VIS), near IR (NIR), and shortwave
IR (SWIR). Optical sensors are commonly used in sea ice
applications, but they are constrained by the availability
of sunlight and a cloud‐free sky in order to be able to
observe the surface. They detect solar reflection using
photographic or digital cameras. Sensors operating in the
MIR and TIR ranges detect the thermal reflection using
films with IR‐sensitive emulsion or spectroradiometers.
Visible spectrum
•
Visible region VIS
(0.4-0.7
μ
m)
- Blue (0.4-0.5
μ
m)
- Green (0.5-0.6
μ
m)
0.4
0.5
0.6
0.7
Wavelength,
μ
m
- Red (0.6-0.7
μ
m)
•
•
Near-infrared region (NIR)
Short-wave IR (SWIR)
0.7-1.3
μ
m
Reflected IR
1. 3-3
μ
m
•
•
•
•
Middle-IR (Mid-IR)
3-8
μ
m
8-15
μ
m
15-1000
μ
m
>1 mm
Thermal infrared region (TIR)
Emitted radiation
(Modeled by blackbody radiation)
Far infrared (FIR)
Microwave region (MW)
Figure 7.1
Categories of remote sensing based on the spectral regions. (For color detail, please see color plate
section).
