Advanced Techniques : CRST(3)
Computational Remote Sensing Technology(continued)
What is remote sensing technology indeed
In the preceding sections, the term: CRST is already motioned. Nevertheless, our understanding remote sensing technology should not be confined to the level at traditional definition and range of GIS, which has produced some misleading information and data. The achievement of CRST at initial stage was gained by means of data transfer. To further understand CRST and discover hidden data and information, our focus should be on the basic concept: What is remote sensing technology indeed?
To fully answer this question, it could be not so easy, which employ massive interdisciplinary knowledge and deep theories. Figure 5 offers us a picture which may be concerned by most relevant researchers in the world. As seen, remote sensing technology is a super large picture if it is considered in detail at both macro and micro level.
In fact, so-called remote sensing technology is a series of process and behaviour, in which various analytical devices are sent into sky and space to carry out various experiments. Such experiments could have following features at high level although the principles of analytical devices are same or similar compared to those performed at ground laboratory:
1. The process of collecting raw data is based on micro-substance thus photon on which remote sensing fully relies. According to the source, the photon can be classified into active and passive photon. The active photon can be further classified into natural and artificial photon. The natural photon is often indicated as solar beam thus sunlight. human-made photon is emitted by a laser device. But in remote sensing, human-made photons are emitted from tubes arranged in the shape of matrix; such device forms SAR. The human-made photons are emitted in one certain time interval (frequency) thus they are emitted in a discrete manner unlike that natural photon travel through space in a continuous manner. They travel at the speed of natural light. The passive photons are generated by polar molecules; thus molecule (e.g. water) has a dipole, therefore water is polar molecule. All micro particles have a unique feature thus particle-wave duality (see Figure 5) . The momentum of particle (electromagnetic wave) can be converted into energy (radiation), nevertheless, the feature of electromagnetic wave can be presented as coexisting electric and magnetic fields which is perpendicular to each other. Electromagnetic wave has the effect of induction on polar and non-polar molecules. Hence an instant dipole is generated by polar and non-polar molecules simultaneously. In terms of quantum theory, a photon is absorbed by molecule accompanying with an electron being jumped higher energy level from the ground energy level. However, the electron is dropped into the lower energy level (may be rolled back ground energy level) accompanying with a photon being emitted out of molecule. The emitted photon refers to passive photon. Both active photon and passive photon have particle-wave duality. This is a very important micro mechanism playing a vital role in remote sensing technology. At this stage, it is necessary to point out that such micro mechanism also exists in LiDAR rather than only being confined to SAR.
2. The condition of experiment completely differs from that at ground laboratory and becomes extremely complicated;
3. The remotely sensed substances are very complicated, not as simple as the sample tested at ground laboratory;
4. A lot of dynamic phenomena have to be considered as either experimental conditions or individual investigated objects;
5. The physicochemical properties must be considered. For instance, water at temperature below 273.15 K becomes solid phase, over 273.15 K changes to be liquid phase. In other words, the phase transition of remotely sensed substance at different season and geolocation must be considered;
6. …
The CRST has been developed on the basis of such micro analysis starting from the initial approach. Accordingly, it has a close relation to the approach of traditional GIS, in addition, owns distinguished and powerful features in both verifying the quality of work of the later and innovating unique techniques.
Figure 5
