Atmospheric window

The interaction between electromagnetic radiation and the atmosphere, such as absorption, scattering and reflection, makes the atmosphere attenuate electromagnetic waves to different degrees in different bands. Generally, the band with low attenuation and high transmittance of electromagnetic waves by the atmosphere is called the atmospheric window (Figure 2- 12). The detection band used in remote sensing should be selected in the atmospheric window in order to receive more electromagnetic wave information from ground targets.

Figure 2-Atmospheric transmittance chart with12 less than 15μm

At present, the commonly used atmospheric windows are as follows.

1. Photography window (0. 3 ~ 1.3 micron)

Namely ultraviolet, visible light and near infrared bands. This band is the best band for photographic imaging, and it is also the common band for scanning imaging of many satellite sensors, such as TM 1-4 band of Landsat satellite and HRV band of SPOT satellite.

2. Near-infrared window (1.5 ~ 1.8 μ m, 2.0 ~ 3.5 μ m)

This band is usually used for scanning imaging under good daylight conditions. For example, TM _ 5 and TM _ 7 bands of Landsat satellite are used for geological mapping or detecting water content of plants.

3. Mid-infrared window (3. 5 ~ 5.5 microns)

This window not only reflects solar radiation, but also the emitted energy of the ground object itself. For example, the AVHRR sensor of NOAA satellite uses 3. 55 ~ 3.93 microns, and get the day and night cloud picture.

4. Far infrared window (8 ~ 14μ m)

This window mainly comes from the thermal radiation energy of the object and is suitable for imaging at night.

5. Microwave window (8 ~ 1000 mm)

The transmittance of this window is 100%, which is one of the main windows for the application of remote sensing technology at present and can work all day. For example, the common band of side-looking radar images is 0. 8cm, 3cm, 5cm, 10cm and so on.

See Table 2-4 for detailed atmospheric windows and remote sensing spectral channels.

Table 2-4 Atmospheric Window and Remote Sensing Spectrum Channel