©2017 Remote Sensing Geoscience and Engineering Consulting
LiDAR & Satellite Incorporated Application(37)
A Studied Case
Theories Invovled in Application (2)
Figure 1
Figure 2
Figure 3
As a matter of fact, many processes occur in leaf can be explained in the terms of quantum mechanics. The photosynthesis relies on the pigments in leaf absorbing solar radiation thus solar photons in VIS region. The residue energy is released in the form of photon. This process is called as fluorescence (see Figure1). This process is happening in a molecule, therefore with a longer wavelength. It can be observed in the region NIR. A similar process could happen within an atom due to electrons being pulled apart and then ionized. The emitted energy is powerful, which can be discovered in UV region. The fluorescence is, in fact, a self-protecting process. It is impossible for the pigments in leaf to absorb solar photons infinitely to raise the temperature in system. For any (bio-) chemical reaction, there is an optimum active energy and temperature. If the temperature exceeds the extreme which catalyst can undergo, catalyst such as enzyme (a kind of protein) will be damaged, then lose its functionality of catalysis. In fact, any catalyst including ones used in industrial production has the similar or same phenomenon. Therefore, the excess energy must be released by means of such as evaporation of water so as to maintain the effective working temperature of a system.
An instant example is given here for ones to easily understand this principle. In daily life, the refrigerator has the same working functionality, but with different working solvent used in evaporation and energy supplier (electricity other than solar radiation).
Fluorescence
Absorption spectra of some photosynthetic pigments
Quantum Mechanics and Spectral Absorption in Leaf
Chemical Structures of Common Pigment in Leaf
There are several pigments involved in photosynthesis, the centre of reaction is always located at a metal ion-molecule complex. Due to metal ion such as magnesium ion (Mg2+) has an unpaired electron in its atomic orbit or unbalanced charge when it shares density of electron with other atom such as nitrogen N being located in other part of chemical structure, it leads to that photosynthesis happens accompanying with electron transfer. That thereby results in a series of redox, and the corresponding products are generated in plant.
Some photosynthetic pigments can be identified from their individual spectrum (see Figure 2). In the micro-state, each atom or functional group has its own spectral feature because each of them is in motion in vibrational mode. Accordingly, the intensities of absorption spectra in different pigments relies on bond energies and their spatial positions in their chemical structures. Therefore, some energy transitions are forbidden, which fail to be found in remote sensing.
The chemical structures and their molar weights of those photosynthetic pigments are shown in Figure 3. Because they are big molecules, the molecular weight is often expressed by unit: amu. The relation of conversion is that 1amu =1 Da = 1 g /mole. It is useful in a specific calculation to be mentioned later (see section 55).
