Il Telerilevamento in AMRA:
Realtà e Prospettive legate alle Attrezzature
Gianfranco Fornaro
Istituto per il l Rilevamento Elettromagnetico dell’Ambiente (IREA)
Consiglio Nazionale delle Ricerche (CNR),
Via Diocleziano, 328, 80124 Napoli
Summary
1. Overview of the remote sensing systems;
2. Optical systems;
3. Microvawe systems;
4. Le attrezzature in AMRA;
AMRA- Sezione di Telerilevamento
Remote sensing
AMRA- Sezione di Telerilevamento
The Photon
Radiation contain photons (units in the EM force field).
The photon is the physical form of a quantum, the basic particle studied in
quantum mechanics. It is also described as the messenger particle for EM force
or as the smallest bundle of light. This subatomic massless particle comprises
radiation emitted by matter when it is excited. It also can become involved as
reflected or absorbed radiation.
Photons move at the speed of light and they also move as waves and hence,
have a "dual" nature.
The amount of energy characterizing a photon is determined using Planck's
general equation:
E=hf
h is Planck's constant (6.6260... x 10-34 Js)
AMRA- Sezione di Telerilevamento
The distribution of all photon energies over the range of observed frequencies
is embodied in the term spectrum. A photon with some specific energy level
occupies a position somewhere within this range, i.e., lies at some specific point
in the spectrum
When any target material is excited by internal processes or by interaction with
incoming EM radiation (a collection of photons), it will emit photons of varying
wavelengths whose radiometric quantities differ at different wavelengths in a
way diagnostic of the material.
Photon energy is received at detectors. The plot of variation of power with
wavelength gives rise to a specific pattern or curve that is the spectral
signature.
AMRA- Sezione di Telerilevamento
The Electromagnetic Spectrum
Depending
distinguish:
of
the
frequency
(wavelength)
•Optical sensors;
•Infrared sensors;
•UV sensors;
•Microwave sensors.
AMRA- Sezione di Telerilevamento
we
Radiometric Quantities
Radiant energy (Q), transferred as photons, is said to emanate in short bursts (wave
train) from a source in an excited state.
This stream of photons moves along lines of flow (also called rays) as a radiant flux
(F) which is defined as the time rate at which the energy Q passes a spatial reference
(dQ/dt). [J/sec = W].
Radiant flux density is just the energy per unit volume/surface (dF/dA or dF/dV).
[Wm-3 or Wm-2]. Flux density as applied to radiation coming from an external source to
the surface of a body is referred to as irradiance (E); if the flux comes out of that
body, it's nomenclature is exitance (M).
Radiant intensity (I=dF/dw) is given by the radiant flux per unit of
dw
solid angle ω (in sr - a cone angle in which the unit is a radian or 57
degrees, 17 minutes, 44 seconds) [Wsr-1]
The radiance (L=dI/dA/cosq) [Wsr-1m-2] is defined as the radiant flux
per unit solid angle leaving an extended source (of area A) in a given
direction per unit projected surface area in that direction. Radiance is
closely related to the concept of brightness as associated with dA
luminous bodies. What really is measured by remote sensing detectors
is radiances at different wavelengths leaving extended areas (which
can "shrink" to point sources under certain conditions)
dw
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q
Radiant fluxes that come out of sources (internal origin) are referred to as radiant
exitance (M) or sometimes as "emittance" (now obsolete). Radiant fluxes that reach
or "shine upon" any surface (external origin) are called irradiance. Thus, the Sun, a
source, irradiates the Earth's atmosphere and surface.
Most wave trains are polychromatic, meaning that they consist of numerous sinusoidal
components waves of different frequencies. The bundle of varying frequencies
constitutes a complex or composite wave. Any complex wave can be broken into its
components by Fourier Analysis which extracts a series of simple harmonic sinusoidal
waves each with a characteristic frequency, amplitude, and phase. All the above
radiometric parameters can be specified for any given wavelength; this spectral
radiometric quantity (which has a value different from those of any total flux of
which they are a part [unless the flux is monochromatic] is recognized by the addition to
the term of a subscript λ, as in Lλ.
EM radiation can be incoherent or coherent. Waves whose amplitudes are irregular
or randomly related are incoherent; polychromatic light fits this state. If two waves of
different wavelengths can be combined so as to develop a regular, systematic
relationship between their amplitudes, they are said to be coherent; monochromatic
light generated in lasers meet this condition.
AMRA- Sezione di Telerilevamento
Interaction
Any beam of photons from some source passing through medium 1 (usually air) that
impinge upon an object or target (medium 2) will experience one or more reactions :
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Blackbody emission
Fundamental laws of emission: Planck (W/m2/mm), Stefan-Boltzman and Wien
equations
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Solar irradiance
The primary source of energy that illuminates natural targets is the Sun. Solar
irradiation (also called insolation) arrives at Earth at wavelengths which are
determined by the temperature of the sun (peaking near 5600 °C). The main
wavelength interval is between 200 and 3400 nm (0.2 and 3.4 µm), with the
maximum power input close to 480 nm (0.48 µm), which is in the visible green
region. As solar rays arrive at the Earth, the atmosphere absorbs or backscatters a
fraction of them and transmits the remainder.
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Processes in atmosphere
Most remote sensing is conducted above the Earth either within or above the
atmosphere. The gases in the atmosphere interact with solar irradiation and with
radiation from the Earth's surface. Although the incoming irradiation is a single
source of excitation of atoms and molecules in the air and any materials found at
the surface, that EMR irradiation will experience varying degrees of transmission,
absorption, emittance, and/or scattering depending on whatever wavelengths are
considered. Here is a general diagram showing the "fate" of this irradiation.
AMRA- Sezione di Telerilevamento
Trasmission in atmosphere
At some wavelengths the irradiation is partly to completely transmitted; at others
those photons are variably absorbed by interaction with air molecules. Here is a
generalized diagram showing relative atmospheric radiation transmission and
absorption at different wavelengths.
AMRA- Sezione di Telerilevamento
Imaging Systems
Imaging sensors are systems, typically mounted on-board
satellites or airborne that are used to “sense” the properties of an
object without being in contact with it.
Depending on the used radiation (information transport media)
there are two main categories:
•passive
•active
and three main characteristics:
•spatial resolution
•radiometric resolution
•spectral resolution
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Sensor Technology
Most remote sensing instruments (sensors) are designed to measure photons. The
fundamental principle underlying sensor operation centers on what happens in a
critical component - the detector. This is the concept of the photoelectric effect: there
will be an emission of negative particles (electrons) when a negatively charged plate
of some appropriate light-sensitive material is subjected to a beam of photons.
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Sensor Technology (cnd)
Most remote sensing instruments (sensors) are designed to measure photons. The
fundamental principle underlying sensor operation centers on what happens in a
critical component - the detector. This is the concept of the photoelectric effect: there
will be an emission of negative particles (electrons) when a negatively charged plate
of some appropriate light-sensitive material is subjected to a beam of photons.
AMRA- Sezione di Telerilevamento
Floods monitoring
24/9/92 before flood
1/8/93 flood peack
Landsat Thematic Mapper (TM) on a portion of the Missouri River Floodplain close to
Glasgow, Missouri.
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Lakes
Landsat multispectral images of Ciad Lake (Central Africa).
Bands 4, 2 e 1 del Landsat, Ciad lake extension between 1973 (left) and 1987 (right).
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Optical High spatial resolution
Optical image, 1 m resolution of Sydney (Australia): IKONOS - 2/7/2000
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Spectral Signatures
For any given material, the amount of solar radiation that reflects, absorbs, or
transmits varies with wavelength. This important property of matter makes it
possible to identify different substances or classes and separate them by their
spectral signatures (spectral curves).
For example, at some wavelengths, sand reflects more energy than green
vegetation but at other wavelengths it absorbs more (reflects less) than does the
vegetation. In principle, we can recognize various kinds of surface materials and
distinguish them from each other by these differences in reflectance.
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Spectroscopy
Imaging spectroscopy, also known as hyperspectral remote sensing, consists of the
simultaneous acquisition of images in many narrow, contiguous, spectral bands. Each pixel in
the remotely acquired scene has an associated spectrum similar to the spectra of a material
obtained in the laboratory. As a result hyperspectral data offers a more detailed examination of
a scene than other type of multispectral remote sensing data, which is collected in broad,
widely separated bands.
AMRA- Sezione di Telerilevamento
Spectral resolution
The resulting hyperspectral data offers a more detailed view of the spectral properties of a
scene than the more conventional broad (spectral) band data, which is collected in wide, and
sometimes non-contiguous bands. Hyperspectral data can be considered as an oversampling of
the spectrum, which provides a great increase in information. Many remote sensing tasks which
are impractical or impossible with a multispectral imaging system can be accomplished with
hyperspectral imaging.
AMRA- Sezione di Telerilevamento
Example of
Spectroscopy
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Spectroscopy
224 Band AVIRIS (Airborne Visible-Infrared Imaging Spectrometer, developed at JPL)
Datacube.
x and y axes represent spatial data (1024 x 614) as a 3 band colour composite image (R
= band 43, G = 17, B = 10). The z axis represents spectral data as 224 contiguous
bands from 0.4mm (foreground) to 2.5mm (background) in pseudocolour (rainbow).
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Vegetation classification
AVIRIS hyperspectral image of some circular fields in the San Juan Valley of Colorado. The
colored fields are identified as to vegetation or crop type as determined from ground data
and from the spectral curves plotted for the crops indicated. These curves were obtained
from the AVIRIS data directly.
AMRA- Sezione di Telerilevamento
Geologic application
The left image shows the area mapped as rendered in a near natural color version; the center
image utilizes narrow bands that are at wavelengths in which certain minerals reflect energy
related to vibrational absorption modes of excitation; in the right image, modes are electronic
absorption. Shown here without the mineral identification key, the reds, yellows, purples,
greens, etc. all relate to specific minerals.
AMRA- Sezione di Telerilevamento
An example on fires
VIS
NIR
FIR
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COMPETENZE
 Modelli di trasferimento radiativo in atmosfera:
Ricostruzione di profili atmosferici di temperatura,
umidità, concentrazione di componenti chimici
 Classificazione di immagini multi- e iperspettrali: riconoscimento di nuvole, campi agricoli
AMRA- Sezione di Telerilevamento
Equazione del Trasferimento Radiativo
(RTE)
Satellite
Radianza
Rs 
 g B (Tg ) 0  
H Sat
0
BT ( z ) 

dz
z
Trasmittanza
R(s)
ds
dz

q
s
 z, z  dz, s ,q 
 z  dz N mol
dz 
 exp    kn s , z n z

z
cos
q
n

1


Coefficiente di assorbimento
monocromatico per la molecola nma
z
Densità della molecola nma
Surface
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Modelli di trasferimento radiativo
Visualizzazione di Jacobiani dell’equazione
di trasferimento radiativo ad altissima
risoluzione spettrale (<0.001 cm-1)
Parametrizzazione degli Jacobiani
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To speed-up radiative transfer models, it is important to parameterize optical
depth as a function of temperature for wavenumbers at a resoluzione 0.001
cm-1
Animation file
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Clouds recostruction
Sensor MODIS (Multispectral)
Spatial resolution: up to 250m
Number of channels: 36
A scene of 1000x600 Km brings about 350 Milions of data
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Clouds
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Vegetation
Sensor MIVIS (airborne)
Spatial resolution: 4 m
Channel: 102
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Laguna di Venezia
Fonte: LARA-CNR
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AMRA- Sezione di Telerilevamento