1. The basic process remote sensing
Remote
sensing an electromagnetic wave is reflected by the information transmitted and is mounted on the platform Remote Sensing by remote detection of objects, analysis and processing procedure to implement remote detection of ground targets.
The basic process of remote sensing are: acquiring remote sensing data - data processing, analysis, data applications
(1) energy
to all passive remote sensing use of energy are solar radiation. The solar spectral range including ultraviolet, visible, infrared, etc., is a comprehensive radiation of different wavelength bands, the intensity of which varies with time and place. Passive sensing is dependent on the surface characteristics of solar radiation reflected or emitted energy itself.
(2) propagating in the atmosphere
solar radiation passes through the atmosphere will be scattered by the particles in the atmosphere and absorbing the energy is attenuated. This decay will make the original continuous spectrum of the sun becomes incomplete. At this point we mention the atmospheric window, the concept, the atmospheric window is at atmospheric absorption is weak, and high transmittance band called the atmospheric window.
(3) reaches the surface energy and surface material interaction
energy of different wavelengths after reaching the surface, the selective reflection, absorption, transmission, refraction, etc.
(4) again atmospheric propagation
of surface energy reflected or emitted by the atmosphere again again energy attenuation. At this time, the more energy is different from the single energy enters the atmosphere, but contains different spectral characteristics of surface energy characteristics. At this time, the influence of atmospheric effects on the sensing large, will cause the radiation image sensing, geometric distortion, image blur, directly affect image clarity, quality, accuracy of interpretation.
(5) electromagnetic wave sensing feature information collecting system
remote sensing system refers to the combination of different remote sensing and remote sensor platforms. There are passive remote sensing systems, active remote sensing system. Different remote sensing systems have their own advantages and disadvantages. Thus, in the use of remote sensing data, they need to understand their characteristics and sources of error, and try to correct the error.
(6) image data products
Wherein the reflective surface of the electromagnetic spectrum and emission recorded remote sensing instruments, there are two forms: an analog image and a digital image
(7) for processing data, analysis and interpretation
are: visual interpretation or analog image processing, digital image processing computer
(8) information
includes variety of graphics, images, image maps, thematic maps, tables, the various parameters (temperature, humidity, biomass, vegetation coverage, surface roughness, etc.), the database files. This information can be combined by means of a comprehensive GIS different levels of analysis, remote sensing and GIS, can significantly improve the accuracy of the information about the product (quality).
(9) Multi-target users
are mainly resource survey, environmental monitoring, land management, regional planning, global research.
2. Remote sensing electromagnetic emission
sensing electromagnetic radiation is a recording image due to the surface interactions. The principle of electromagnetic radiation through the atmosphere and the process is again reflected by the surface, is the basis of remote sensing.
(1) Measurement of electromagnetic radiation
by remote sensing to detect objects, and in fact the analysis of the measured object radiated energy.
Radiation energy: refers to electromagnetic energy in the form of an object conveyed outward. Q commonly expressed in units of J, cal
radiant flux: also known radiation power, refers to the unit of time, by the energy of a surface.
Degree of radiation emitted: also known as radiation flux density, refers to the surface in unit time the radiation source, the radiation from the radiation energy per unit area, i.e., the object emits radiation flux per unit area.
Irradiance: Irradiance referred to, refers to the surface within a unit of time the radiation source, the radiation energy per unit area received from, i.e., irradiated radiant flux per unit area on the object.
Radiation intensity: pointing the radiation source unit solid angle, the radiation energy per unit time, the light emitted in one direction, i.e., point source of radiation emitted in the radiation flux per unit solid angle.
Radiance: Radiance referred to, refers to the surface in the radiation source unit solid angle per unit time, in the vertical direction of the radiation per unit area (normal area) of radiation at a radiation energy, i.e. surface area per unit projected on the radiation source unit radiative flux within the solid angle.
(2) the law of electromagnetic radiation
Planck's law of radiation
is blackbody relationship between temperature and degree of radiation emitted, the wavelength of the law describes. Planck's radiation law is a basic law of thermal radiation theory, it shows only depends on the temperature and blackbody radiation wavelength and the emission angle, regardless of internal features.
Stefan - Boltzmann law
any radiation energy of an object is a function of the size of the surface temperature. Proportional to the fourth side absolute temperature of the object of the total energy emitted by the object. Thus, with increasing temperature, radiant energy increase is very rapid.
Wien's displacement law
Wien's displacement law describes the quantitative relationship between the temperature of the radiation peak wavelength of the maximum energy of the radiation object. Absolute temperature of the blackbody radiation intensity corresponding to the maximum wavelength is inversely proportional to the blackbody.
Kirchhoff's law
Kirchhoff's law can be described as, at any given temperature, and the ratio of the emission rate of absorption per unit area on the object, any feature is a constant, and equal to the area of the same below the temperature ratio of blackbody radiation emitted degrees.
(3) Solar radiation
sun is a source of electromagnetic radiation is the main source of remote sensing.
Solar radiation spectrum extends from X-rays to radio waves, is a comprehensive spectrum.
Solar spectrum in the UV, near-infrared band is the main use of remote sensing.
After the sun spectrum in different bands of atmospheric attenuation is not the same.
Atmosphere reaches the Earth's outer boundary of the solar radiation, cloud cover, and about 30% is reflected back into space other atmospheric constituents: about 17% of the incident solar radiation is absorbed by the earth's atmosphere; and 22% is scattered becomes diffuse reflection reaches the earth's surface. Thus, only 31% as direct sunlight, directly into the Earth to reach the surface at the outer boundary of the solar radiation.
(4) terrestrial radiation
Earth radiation can be divided into:
long-wave radiation (more than 6um): refers to the heat radiating surface of the object itself, the influence of solar radiation in this region is extremely small
shortwave radiation (0.3um ~ 2.5um): refers to the earth's surface reflected radiation of the sun , the heat radiation of the earth itself is negligible
interposed between the two infrared radiation (2.5um ~ 6um): both of the reflected solar radiation but also radiation heat of the earth itself, its influence can not be ignored
(5) electromagnetic waves the interaction with the atmosphere
the atmospheric effects
of electromagnetic waves interaction with the atmosphere mainly two basic physical processes: atmospheric absorption and atmospheric scattering
atmospheric scattering
mainly Rayleigh scattering, Mie scattering, scattering non-selective
Rayleigh scattering: scattering caused when when the particle diameter is much smaller than the atmospheric incident wavelength, Rayleigh scattering occurs
Rayleigh scattering characteristics:
fourth inversely proportional to the wavelength of the Rayleigh scattering intensity;
the same backscattering strength to the front and the rear scattered Rayleigh scattering;
Rayleigh scattering occurred in cloudless high altitude;
Mie scattering: when the diameter of the atmosphere caused by the scattering particles is approximately equal to the incident wavelength, Mie scattering occurs
Mie scattering characteristics :
Square of scattering intensity is inversely proportional to the wavelength;
forward scatter is greater than the backscatter;
Mie scattering occurs in wet weather;
non-selective scattering: scattering produced when the diameter of the atmosphere caused by the incident particles is much greater than non- selective scattering
atmospheric clouds, fog, droplets, dust scattering belong to such
influence of atmospheric scattering on remote sensing images is extremely large, the main attention is what we need at the time of correcting the image sensing
atmospheric absorption
of atmospheric air in addition to scattering, further there atmospheric absorption, so that energy is attenuated
Atmospheric absorption is mainly caused by the three kinds of air molecules. They are ozone, carbon dioxide, and water vapor.
Atmospheric attenuation: atmospheric attenuation means when the electromagnetic wave propagation in the atmosphere due to absorption and scattering intensity decreased to make the atmosphere. Reduced light intensity caused thereby, also known as matting.
(6) atmospheric correction
Why atmospheric correction?
Sensing radiation are utilized for a variety interacts with the Earth's atmosphere, so that the spectral distribution changes, and because the electromagnetic wave is acquired feature information, the different geometric path, atmospheric effects are also different. To eliminate the influence of the atmosphere on the sensing signal, called atmospheric correction.
Atmospheric correction are: the model image feature ground linear regression model, the theoretical atmospheric radiative transfer model
(6) the main object of the three forms of electromagnetic waves reflected
specular reflection: Assuming surface with respect to the incident wavelength is smooth, specular reflection occurs . Of still water, smooth metal surface specular reflection can occur, specular reflection component is a phase coherent and polarized with
diffuse reflection: when the incident energy is reflected uniformly in all directions. If the surface is rough relative to the incident wavelength, i.e., when the incident wavelength or smaller height h than the surface material particle size, than surface diffuse reflection occurs. Diffuse irregular amplitude and phase variation
direction of the reflection: reflecting feature is neither practical nor specular reflection is diffuse reflection, where the concept of lead BRDF
two reflectivity factor (the BRF): under certain conditions of exposure and observation, target the ratio of reflected radiation flux reflected radiation flux of a standard reference plane (the ideal Lambertian surface) under the same conditions of exposure and observation in
reflectance: all the incident radiant energy than the energy of the target reflected in all directions, it It can be seen as integral surface reflected in all directions.
*** above refer to "Remote Sensing Application Analysis Principles and Methods" Zhao Ying, the second edition
