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First, what is remote sensing?
Remote sensing refers to a non-contact, long-range detection technique. Is a combination of telemetry and resource management monitoring of the Earth's surface (resource management such as trees, grasslands, soil, water, minerals, farm crops, fish and wildlife) through telemetry on artificial Earth satellites New technologies. Remote sensing technology has the advantages of large coverage area, short revisit cycle and relatively low acquisition cost, and plays a unique role in the investigation, evaluation, monitoring and management of large-scale open-air agricultural production.
Second, the development of agricultural remote sensing
Since the popularization of civil resources satellites in the 1970s, agriculture has become the first field where remote sensing technology is put into applications and benefits significantly. Especially with the advent of high-spatial, hyperspectral and high temporal resolution remote sensing data, agricultural remote sensing technology has made breakthroughs in key technologies such as long-term sequential monitoring of crop growth, subdivision of crop species, access to fine agriculture information in the field. Agricultural remote sensing monitoring mainly uses crop and soil as objects, and uses the spectral characteristics of the ground objects to monitor crop growth, crop quality, crop pests and diseases.
Since remote sensing technology has the characteristics of large coverage area and short revisit cycle, it is mainly applied to the investigation, evaluation, monitoring and management of large-scale agricultural production. Its application in agriculture is classified into the following four categories according to the content:
1, agricultural resources survey. Including the investigation of current resources such as cultivated land resources and soil resources, as well as the dynamic monitoring of land desertification and salinization, farmland environmental pollution and water and soil loss, etc., providing the quantity, distribution and changes of various resources as well as various resource evaluation based on surveys, Proposed measures should be taken for the organization, management and decision-making of agricultural production.
2, crop yield estimation. Including wheat, corn, rice, cotton and other bulk crop growth monitoring and yield forecast, including the estimation of pasture grass production, fruit tree growth monitoring.
3, agricultural disaster forecast. Including crop pests and diseases, freezing damage, floods and droughts, dry hot wind and other dynamic monitoring, as well as post-disaster farmland damage, crop loss and other loss surveys and assessments.
4, precision agriculture. The main objective is to investigate the current situation of farmland area and distribution using satellite data with high spatial resolution and to monitor crop growth, pest and disease and soil moisture on farmland-scale cropland for precision fertilization, application and irrigation.
5, for different applications, different spatial resolution of optical remote sensing and microwave remote sensing have different advantages. For example, high spatial resolution remote sensing data mainly uses field-scale precision agriculture, and high temporal resolution wide-coverage remote sensing data is mainly used for monitoring the growth of large-scale crops. According to the characteristics of various types of remote sensing data, its main application areas are shown in Table 1.
Third, the development trend of agricultural remote sensing technology
1, a new generation of agricultural UAV technology
Unmanned aerial vehicle (UAV) is a kind of new remote sensing platform driven by power, unmanned and reusable on the aircraft, which has the advantages of flexibility and real-time superior to other remote sensing platforms. Especially, with the miniaturization of visible-near-infrared aerial imaging spectrometer and aerial CCD digital camera, the visible-near-infrared image with centimeter-class spatial resolution can be obtained at any time. Therefore, the present application of the remote sensing system to environmental protection, agriculture, disaster relief And other applications have been rapidly expanding.
Due to the influence of weather, orbital period and spatial resolution, agricultural satellite remote sensing technology still has many deficiencies in the field-scale agricultural monitoring. It is often difficult to provide high-quality remote sensing data in time. UAV remote sensing can be used in conjunction with large-area satellite remote sensing Cooperate with each other to form multi-scale agricultural information monitoring network. UAV remote sensing can take advantage of the fine scale and dynamic continuous monitoring of farmland. It can be applied to the investigation of the boundary and area of ​​farmland plots, the identification and statistics of crop types, crop growth analysis, crop nutrient and soil moisture monitoring, especially after agricultural disasters Evaluation, UAV remote sensing technology will play a unique role.
2, agricultural ground sensing network and remote sensing technology
At present, all kinds of ground-based observation technologies and network construction based on wired and wireless sensors are gradually developed and perfected, which provide important authenticity information for the retrieval of surface parameters, model assimilation and coupling, and accuracy verification of satellite remote sensing. In the field of agriculture, agricultural ground sensing networks based on modern Internet of Things technologies have been rapidly applied in the management of smart greenhouses and field operations. In particular, various types of sensors that automatically collect crop foliage to the canopy, physical and chemical information from the surface to the surface, and environmental information such as temperature, humidity and light in the farmland are constantly appearing. Coupled with the wireless transmission network and the intelligent control system, The convenience, accuracy, timeliness has been significantly improved.
3, agricultural professional model and remote sensing technology coupling
Remote sensing technology has the advantage of providing a large range of earth observation data in multi-scale, multi-band and multi-realities, and can timely obtain surface characteristic information such as vegetation index, brightness index and surface radiation temperature, and further obtain by quantitative inversion Surface characteristics such as surface reflectance, leaf area index, soil moisture content and so on. However, remote sensing of agriculture, especially remote sensing monitoring of crops, crop height, leaf area, biomass and other key attributes in the growth period is a dynamic process of continuous changes, it is difficult to ensure the continuity of observations by remote sensing data alone. Therefore, a large number of researches focus on coupling or assimilating agricultural professional models such as crop growth model and surface energy balance model with remote sensing data to make up for the shortcomings of time resolution of remote sensing observations.
The new trend is to improve the applicability of the traditional agricultural professional model, to overcome the model completely to farmland plots as a sample, less consideration of the shortcomings of the spatial heterogeneity of features; the second is to play the advantages of multi-source data, combined with the ground Sensitive network to improve the periodicity of information collection; Third, the standardization of remote sensing data products and business-oriented, such as MODIS series of data products, business can provide 8 d vegetation index, leaf area and other data products, making traditional agronomists easier Remote sensing data is introduced into various agricultural professional models.
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