Relationship between spatial resolution and optical transfer function
For a given geological unit, such as a basic pixel size with ground characteristic distribution or characteristic field, according to the basic radiation law, the radiance L reaching the sensor entrance pupil can be described by its spatial, spectral, and temporal distribution characteristics:
L input=f (x, y, z; λ; τ; t) (5-5-2)
In the formula, x, y, and z represent spatial positions; λ is the wavelength; T represents time; τ represents the transmittance of the atmosphere. F represents the functional relationship between the interaction between the incident light and the atmosphere before reaching the entrance pupil of the sensor, the reflection characteristics of the geological body, and the radiation energy of each part of the reflection radiation of the geological body and the interaction with the atmosphere.
During the imaging process, the sensor optical system spatially samples the signal, dividing it into discrete pixels or pixels on the image
L light=f (x, y, z; λ; τ; t; MTF; S λ) (5-5-3)
MTF represents the modulation transfer function of the optical system, the spectral response function of the S λ detector (also known as the transfer function of the detector), and L light represents the spectral radiation value output by the optical system. Another factor that determines spatial resolution is the modulation transfer function (MTF) of the optical system, which affects the resolution and contrast of the image. The level of modulation transmission is the standard for evaluating image quality. The optical system's conversion process of the incident spectrum is actually the modulation and transformation process of the modulation transfer function on the incident light.
5.5.2.1 Radiation measurement
The measurement of radiation power and energy from optical remote sensing of the ground from space can be simplified into the process shown in Figure 5-5-1. In general, assuming the intersection angle between the axis of the sensor and the surface normal of the ground radiation source is θ, and the half angle of the incident pupil of the sensor to the radiation source is a (Mai Weilin, 1979). At this point, the surface size of the detector element acts as a field of view aperture, limiting the field of view that the sensor can observe. The geometric projection of the field of view aperture on the ground corresponds to the ground resolution element, as indicated by the dashed line in Figure 5-5-1 (b). The instantaneous field of view half angle is represented by β. The angles α and β have a significant impact on the energy harvesting characteristics of incoherent radiation sources.
