The concept of waves: Waves are the propagation of vibrations in space.

RS refers to electromagnetic wave remote sensing

The reason why remote sensing can judge ground objects and natural phenomena based on collected electromagnetic waves is because all objects have completely different electromagnetic wave reflection or emission radiation characteristics due to their different types, characteristics and environmental conditions.

The chart made by arranging the wavelengths of electromagnetic waves is called the electromagnetic spectrum.

The order is: γ rays - X rays - ultraviolet rays - visible light - infrared rays - microwaves - radio waves.

Radiation energy (W): The energy of electromagnetic radiation, unit: J.

Radiation flux (Φ): Radiation energy passing through a certain area per unit time, unit: W.

Radiation flux density (E): Radiation energy passing through unit area per unit time, unit: W/m2

Irradiance (I): Radiation flux per unit area of ​​the surface of the radiated object, unit: W/m2

Radiation exit (M): Radiation flux per unit area of ​​the surface of the radiation source object, unit: W/m2.

Solar constant 1367±7 W/m2

Radiant brightness (L): The radiation flux of the radiation source in a certain direction, unit projection surface, unit solid angle, unit W/(sr·m2)

color

saturation

brightness

Achromatic colors only differ in brightness, without the two characteristics of hue and saturation.

The selection condition of the three primary colors is that any one of the three primary colors cannot be mixed by the addition of the other two; the method of using them to synthesize colors is simple and stable, and more colors can be synthesized. Red (R)——0.7um Green (G)——0.5461um Blue (B)——0.4358um

absolute black body

Black body radiation law--Planck's formula

Black body radiation law - Stefan-Boltzmann law

Black body radiation law--Wien's displacement law

inference

The solar spectrum is closest to the black body radiation of 5777K (6000K)

The energy of solar radiation is mainly concentrated in visible light, of which the visible light energy between 0.38 and 0.76 µm accounts for 46% of the total solar radiation energy, and the maximum radiation intensity is located at a wavelength of about 0.47 µm;

The solar radiation reaching the ground is mainly concentrated in the 0.3-3.0 µm band, including near-ultraviolet, visible light, near-infrared and mid-infrared;

The attenuation of each band is uneven.

Solar radiation passing through the atmosphere is greatly attenuated;

Earth radiation is equivalent to black body radiation close to 300K

Troposphere: 7 to 12 km. The temperature decreases with altitude and the weather changes frequently. Aviation remote sensing is mainly in this layer.

Stratosphere: 12 to 50 km. The bottom is the stratosphere (aviation remote sensing active layer). Above the stratosphere, the temperature gradually increases due to the strong absorption of ultraviolet rays by the ozone layer.

Ionosphere: 50 to 1,000 km. O2 and N2 in the atmosphere are ionized by ultraviolet irradiation and are transparent to the remote sensing band. It is the active space of land satellites.

Outer layer of atmosphere: 800~35,000 km. The air is extremely thin and has basically no impact on satellites.

atmospheric composition

The effect of oxygen on electromagnetic waves is in the range other than ultraviolet light (<0.2um).

Ozone has a strong ability to absorb electromagnetic waves less than 0.3um (<0.3um)

Carbon dioxide: 2.8, 4.3, 14.5um strong absorption bands

Water vapor: mainly concentrated in infrared and microwave bands

The concept of scattering: a phenomenon in which electromagnetic waves deviate from their original propagation direction after the interaction between electromagnetic waves and matter.

Rayleigh scattering (molecular scattering): d <<λ

Mie scattering (aerosol scattering): d ≈ λ

why is the sky blue

Why are morning glow and sunset glow red?

Characteristics of atmospheric scattering

The relationship between atmospheric scattering coefficient and altitude

Concept: When solar radiation is transmitted through the atmosphere, reflection, absorption and scattering jointly attenuate the radiation intensity, and the remaining part is the transmitted part.

Each band of solar radiation is affected by attenuation in different degrees, so the transmittance of each band is also different.

When electromagnetic waves pass through the atmosphere, they are less reflected, absorbed and scattered, and the band with higher transmittance is called the atmospheric window. (Part used for earth remote sensing)

In the visible and near-infrared bands, 30% of solar radiation is reflected by clouds or other particles, 22% is scattered, 17% is absorbed, and 31% of the energy reaches the ground.

The interaction between solar radiation reaching the ground and the surface P0 Reflection Pρ Absorption Pa Transmission Pt P0= Pρ Pa Pt

Reflectivity ρ= Pρ/ P0×100%