LiDAR_&Satellite_Application

Any incident beam will be attenuated while photons travel in any solution. Lambert-Beer’s Law is used to describe this process (see Figure 1 and 3). In the case associated with leaf, as well known, there are much water existing in the vacuoles of leaf, which are up-taken (pumped by leaves) from root system through xylem. Therefore, the equation can be also applied to this case when solar photons are absorbed by chlorophylls.

However, Lambert-Beer’s equation is one describing an overall process of adsorption. It requires a specific molar extinction coefficient for one solution if it is applied to investigating the properties of one solution (see Figure 4). In the most cases, it relies on experiment to gain such a coefficient. This is a limitation of using it.

There are, at least, two important classical theories used to depict the attenuation of light in micro state. They are

1. Statistical thermodynamics. It focuses on how the degree of molecular collision is altered at different energy states. In the statistical thermodynamics, there is a useful concept: entropy, which is also widely used in biochemistry to express how molecular structure is changed, and molecular motions. It also contains a concept of free path of molecule. Generally speaking, the shorter free path, the (bio-) chemical reaction is easily taken place. Studying micro statistical thermodynamics is useful for us to quickly understand macro thermodynamics. The calculation and its result is a most interesting topic for most researchers in the remote sensing field.

2. Quantum chemistry. On the basis of a fact that the energy levels of electrons moving around nuclei in molecules must be altered after solar photons being absorbed by water and pigments in leaf.

However, if combining them with Lambert-Beer’s Law, the unique advances in practice are presented.

• It is seamlessly connecting macro phenomena to micro motion of fine particles.

• It is much easier for us to understand this process and calculate quantitatively.

• Such a process is also liked to the corresponding spectral change by means of finding out the corresponding geo-points of sampling.

However, in this approach, it should be noticed that the concept of system, canonical ensemble and energy level is a term with special meaning in individual discipline respectively. Thus, in micro state, fine particles: molecule, atom and ion including photon are located into an arbitrarily designed system respectively. This abstract concept is based on a substantial fact. Hence, motion of a large number of fine particles in the micro state can be measured and observed in the macro state by means of devices in lab including those in remote sensing.

A quick instance for ones to easily understand this approach is supplied here. In the daily life, the lid must be floating up when water is boiling at 100℃ and 1 atm. That is because the lid undergoes a pressure caused by a large number of quickly moving gaseous water molecules against it while liquid water molecules in a container is being heated up to a boiling point.

This is the philosophy of research.