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Summary Overview of the remote sensing systems; Optical systems;

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Presentation on theme: "Summary Overview of the remote sensing systems; Optical systems;"— Presentation transcript:


2 Summary Overview of the remote sensing systems; Optical systems;
Microvawe systems; Le attrezzature in AMRA;

3 Remote sensing

4 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. E=hf h is Planck's constant ( x Js) The amount of energy characterizing a photon is determined using Planck's general equation:

5 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.

6 The Electromagnetic Spectrum
Depending of the frequency (wavelength) we distinguish: Optical sensors; Infrared sensors; UV sensors; Microwave sensors.

7 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 solid angle ω (in sr - a cone angle in which the unit is a radian or 57 degrees, 17 minutes, 44 seconds) [Wsr-1] dw 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 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 q dA

8 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.

9 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 :

10 Blackbody emission Fundamental laws of emission: Planck (W/m2/mm), Stefan-Boltzman and Wien equations

11 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.

12 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.

13 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.

14 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

15 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.

16 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. The two broadest classes of sensors are Passive (energy leading to radiation received comes from an external source, e.g., the Sun) and Active (energy generated from within the sensor system, beamed outward, and the fraction returned is measured). Sensors can be non-imaging (measures the radiation received from all points in the sensed target, integrates this, and reports the result as an electrical signal strength or some other quantitative attribute, such as radiance) or imaging (the electrons released are used to excite or ionize a substance like silver (Ag) in film or to drive an image producing device like a TV or computer monitor or a cathode ray tube or oscilloscope or a battery of electronic detectors (see further down this page for a discussion of detector types); since the radiation is related to specific points in the target, the end result is an image [picture] or a raster display [as in:the parallel lines {horizontal} on a TV screen). Radiometer is a general term for any instrument that quantitatively measures the EM radiation in some interval of the EM spectrum. When the radiation is light from the narrow spectral band including the visible, the term photometer can be substituted. If the sensor includes a component, such as a prism or diffraction grating, that can break radiation extending over a part of the spectrum into discrete wavelengths and disperse (or separate) them at different angles to detectors, it is called a spectrometer. One type of spectrometer (used in the laboratory for chemical analysis) passes multiwavelength radiation through a slit onto a dispersing medium which reproduces the slit as lines at various spacings on a film plate. The term spectroradiometer tends to imply that the dispersed radiation is in bands rather than discrete wavelengths. Most air/space sensors are spectroradiometers.

17 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.

18 Landsat multispectral images of Ciad Lake (Central Africa).
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).

19 Optical High spatial resolution
Optical image, 1 m resolution of Sydney (Australia): IKONOS - 2/7/2000

20 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.

21 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.

22 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.

23 Example of Spectroscopy
Laurel leaf (foglie di alloro) Talco minerale terriccio

24 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).

25 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. Barley: orzo Oat Hay (Avena)

26 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.

27 An example on fires VIS NIR FIR

28 COMPETENZE Modelli di trasferimento radiativo in atmosfera: Ricostruzione di profili atmosferici di temperatura, umidità, concentrazione di componenti chimici Classificazione di immagini multi- e iper-spettrali: riconoscimento di nuvole, campi agricoli Qui sono indicate secondo il tuo schema le competenze

29 Equazione del Trasferimento Radiativo (RTE)
Satellite Radianza R(s) ds s q Trasmittanza dz Si parte da satellite che misura la radianza emessa dalla superficie terrestre e modificata dai parametri di superficie e atmosferici; viene poi rappresentata l’equazione di trasferimento radiativo (vale a dire l’espressione della radianza) e l’espressione della trasmittanza; ambedue mostrano la dipendenza dalla temperatura e dalla concentrazione dei costituenti chimici alle diverse altezze atmosferiche. Per finire a sinistra in basso viene sovrapposta una famiglia di curve di profili atmosferici di temperatura e costituenti chimici in atmosfera; infine in alto viene riportato lo spettro misurato dal satellite e le curve di corpo nero a diverse temperature. Coefficiente di assorbimento monocromatico per la molecola nma z Densità della molecola nma Surface

30 Modelli di trasferimento radiativo
Visualizzazione di Jacobiani dell’equazione di trasferimento radiativo ad altissima risoluzione spettrale (<0.001 cm-1) Parametrizzazione degli Jacobiani Competenza sui medelli di trasferimento radiativo in atmsofera: esigenza di visualizzare gli Jacobiani rispetto alla temperatura atmosferica, al vapore acqueo e a i costituenti atmosferici; esigenza di parametrizzare gli Jacobiani

31 Visualizzazione degli Jacobiani
Visualizzazione degli Jacobiani. Si osservi che la risoluzione spettrale è cm-1

32 To speed-up radiative transfer models, it is important to parameterize optical depth as a function of temperature for wavenumbers at a resoluzione cm-1 Animation file Parametrizzazione degli Jacobiani: l’interpretazione dei dati ad una risoluzione spettrale così elevata (0.001cm-1) è avvantaggiata dalle tecniche di animazione utilizzate

33 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 Esempio dell’importanza della visualizzazione nella ricostruzione di nuvole da immagini multispettrali. Dati del sensore MODIS. Per una regione che all’incirca ricopra l’Italia, occorrono circa 350 Milioni di dati. Nei problemi di classificazione è importante andare a vedere come si distinguono le classi nelle varie variabili. Pertanto si visualizzano i dati secondo coppie di variabili (dopo è mostrato un esempio)

34 Clouds Qui viene mostrato un esempio di visualizzazione: per diversi tipi di superficie (terra, mare, deserto) si riporta su un grafico la radianza o riflettanza misurata in condizioni di cielo sereno (rosso) o nuvoloso (blu) per un canale spettrale. L’analisi va poi ripetuta per gli altri canali spettrali per individuare “a occhio” i canali spettrali che distinguono meglio le classi sereno/nuvoloso ed anche per risontrare eventuali anomalie negli algoritmi di classificazione.

35 Vegetation Sensor MIVIS (airborne) Spatial resolution: 4 m
Channel: 102 Seconda apllicazione della classificazione: ricostruzione del tipo di vegetazione da dati telerilevati da aereo

36 Laguna di Venezia Immagine della laguna di Venezia Fonte: LARA-CNR

37 Risultato della classificazione

38 Visualizzazione delle radianze misurate per coppie di bande spettrali: questo tipo di grafico, ripetuto su molte coppie, indica qualitativamente quali sottoinsiemi di canali sono significativi per distinguere tra le varie classi.

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