Forest ecosystem is the main component of the terrestrial biosphere, and the estimation of forest biomass is a necessary condition for the analysis of carbon cycle and regional carbon budget in land ecosystem. As an active detection method, space borne Lidar can directly obtain the information of vertical structure of vegetation, and its retrieval of forest biomass has obvious advantages compared with optical and microwave remote sensing methods. The Lidar obtains the forest three-dimensional structure through the discrete radiation of the echo data in the spot, and then collectively invert the amount of the forest biomass and its spatial distribution pattern through a number of discrete sampling data in a certain region. Obviously, the density of Lidar discrete sampling points is an important factor that determines the fine degree of forest biomass and its spatial distribution pattern. The first generation vegetation measurement Lidar uses linear detection system, which has a large power consumption, limited power supply capacity, and volume and heat dissipation of the satellite platform. The density of the observation point is low, usually 1 to 2 points per square kilometer, which leads to the poor mapping ability of the regional forest biomass. In order to solve the low density of observation points and improve the mapping ability of Lidar in the region of forest biomass, this paper proposes a kind of second generation of vegetation Lidar based on few-photon mode. The application background, the principle of small photon detection and the composition of the system is discussed. The demand for the energy of the laser emission pulse is lower than that of the linear system. Under the condition of the same resource on the satellite, the density of the sampling point is higher than that of the linear system. Therefore, the second generation vegetation Lidar can better depict the number and spatial distribution pattern of regional forest biomass.
Aerosol plays a very important role in the global climate. Due to its short life, changeable sources and sinks and complex physical and chemical and optical properties, it is urgent to grasp the changing trend and its impact on the environment in a large scale through satellite remote sensing technology. This paper expounds the theoretical basis of aerosol detection, introduces the progress of aerosol detection, and puts forward the related technologies of satellite remote sensing to observe atmospheric aerosol.
The Domestic Spaceborne Lidar as a pivotal method in satellite remote sensing is introduced, including the development status and the key technology. By analysing the Lidar system design among the weighted Chang’e-1, resource satellite, the expectation of Spaceborne Lidar Development is released.
Space borne laser altimeter is able to measure the distance between satellite and land surface. Combining with the attitude, orbit and equipment placement information, the elevation of the measured area can be calculated, which can be used as an elevation control point in mapping. By the influence of satellite orbit height and laser spread angle, the footprint of laser on the land surface is in diameter of tens of meters. For the situation of a flat surface, every point has equal elevation and the central point of the footprint can be chosen as an elevation control point. For the situation of undulating surface, each point has different elevation, and there will be much error if the central point of the footprint is chosen as an elevation control point. Now, the point in latter situation is excluded which makes the efficiency of laser altimeter low. In this paper, the situation of undulating surface is considered, and new approaches of using DSM and image recognition are adopted, resulting in acquiring elevation control point in this situation and increasing the efficiency of laser altimeter.
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