Zhang Wei, Yan Tailai, You Shucheng
Remote Sensing Center of China Agricultural University Beijing 100094, China
It could be said that there is no other country in the world has got the situation and background like China. The resources for the development are so critical and so seriously: great population, nearly 22% of the world total, and short agri land, only 7% of the globe agri land which is a very valuable un-renewable natural resources. In one hand, the agriculture was asked to produce enough food to feed people and the other the strongly inquiry for the development, the sustainable development, and further more: the environment conservation and much other aspect we must to dial with.
It is no doubt that the Key-Link for the Chinese economy sustainable development is agriculture not only for the Chinese politicians, economists, but also for the common people. This point of view, that the development of China is not only concerned with Chinese people but also with the world business, is unnecessary to be discussed for many foreigners. It is very clear that:
- China doesn’t like Singapore, Israel, and even Japan. The quantity of population of China, according to the statistic, had reached to 1.2 billion in 1995. Some scientists forecast that number will be about 1.6-1.7 billion in 2030. They are living on the agriculture. They need food, so many foods! No one country could support these necessities.
- The economy development level of China is not very high although it has achieved a very great development. But, in the foreseeable time, it has not got enough hard currency to import food if copy Japan’s model.
- The family land renting-production system had deeply changed the agricultural development of China in the past 20 years. The farmers have got enough free right for planting, don’t need to follow the planning of the government like before. More and more people to be saved (good or bad?) to migration to the city. It was reported in 1987 that some millions or ten millions was going to the city or town and finding a job and better life. Some new villages are established on the suburbs of the big cities.
Population land and agri. Land
|Agri Land(h/per person)||0.2||0.12(wld: 0.32)||< 0.08|
|Agri Land Decrease
(h/per Year, 1980-1995)
|Pop. Increase (per Year)||15 million|
|Chinese population: 22% of the world total
Agri land: 7% of the globe’s
From the above table, you can understand that in China, HOW VALUABLE THE AGRI. LAND IT IS!!!
Land use Survey and Agri. Survey
The results of the development are certainly not to be protected: The City Expanding, and the agri-land to be occupied. The critical problems are the agriculture land is very limited, and if it is occupied or changed into the other using model, they could not easily to be recovered into the agriculture production again.
The territory of China is very big, just equal to the US. But the agricultural land is only 1/4 of the world average per person.
According to the report, in the past ten years, since 1985, with the development and urbanization, 600,000 hectares land were occupied each year. Most of them are fertilized agri. land. It is nearly 0.5% each year of total agri. land. There is only less than 0.1h agri land per Chinese person at the present time.
It had still not stopped this trend although the central government established the National Land Management Bureau who’s responsibility is to make the land, especially the agri land, survey, and to manage and to plan the land use. So, just a few weeks ago, a VIP of the government strongly asked the relevant organizations and institutes to estimate and monitor the land use and land cover every 24 hours. So big works!
The land degradation, Desert and Gobi, drought, flooding and the other disasters are very severely in China. The total areas of the degradation had reached to 1.53 million square km, 15.9% Total areas. In the past ten years, deserted land is: 2,100 s.km/per year. In future 10 years, it will increase to 2,300 s.km/per year if doesn’t take effective actions. The soil erosion areas can’t be estimated. You can see how big problems it is on the land use in China, and so does the populations and food production.
The agri-production structure, means the rate of the different type of the crops, the food plants like wheat, corn or rice and the economical plants like cotton, beans. The government must know earlier the production live so that to prepare the food for the people even some of them had moved to the cities. We need a very fast, very effective, and very economical methods to make the land using and land cover survey, and also the crops survey.
We must have to deal with this kind of crisis with remote sensing. The SAR systems, and only SARS is the best one of them, can play a very important role in these kinds of work.The RS Data and The Advantages of Sars
Remote sensing, especially the sattelite remote sensing, is a new very useful methods for the human to oberve the earth. The imformation which were extracted from the RS data are very helpful for the government and agencies to make the decision,or for the farmers to manage the agricultural productions. The data, for example Mss, TM, Spot… are widely used in the agri survey.
Although the remote sensing application is very beneficial in some aspects: geology, geography, hydrology, and forestry… but does not satisfied in the agriculture with the remote sensing characteristics.
The RS data requirement could be said: very critical. For the agricultural survey, the timingly effectiveness of the remote sensing data is very strictly. If can’t get necessary data in time, it may main a lot of money or goods to be loosed. It is very sad that the remote sensing data we usually used are not fulfilled the requirement of the agricultural survey.
The timing effectiveness requirement for the remote sensing data (re-orbit period) .
|agri. resources manag.||1-2 years|
|crops survey: crops area survey||2-3 mons|
|crops growth stat.||1 mon|
|crops yield estim.||15 days|
|disaster survey: pests||3-5 days|
|agri. sustain develp:
(resources sustainable use)
|agri. environment survey||3-6 mons .|
The Effectiveness analysis for the TM data (Beijing Ground Receiving Station)
But, it is very sad that the RS sensor’s which works on the visual or the infrared bands are affected by the weather conditions and the time, day and night, changing. We choose 8 sites which nearly covered the whole country and to investigate the qualified remote sensing data in the past 10 year since Beijing Remote Sensing Satellite Ground Receiving Station established in 1986. According to the statistics, the effectiveness of the remotely sensed data is very low for the agricultural survey. It is, in China, only 3% -5% in the north areas and even 1%-3% in the southern part in the crops growing seasons. Most of the scientists who working on the agriculture remote sensing survey have these experiences: very difficult to find one scene of the remote sensing data each year. The table shows that the results based on the 8 areas, which nearly spread all over the country. In this condition, how could the remote sensing play well in the agricultural survey?
The signals of remote sensing system which works on the microwave bands could panetrate the clouds freely, not affected by the weather conditions and times changing, day and night.The SARS, SAR Remote Sensing , with un-insteadable characteristics: the real time, all weather and climate conditions data collection capabilities and the other unlimited or unexpected power, will surely play a key role in the agriculture and land survey.
In the past 5 years, a very big progress have been taken in the Radar remote sensing field. At the present time some remote sensing imaging Radar systems are opperating, or will be lauched in near future.
The Case Study
The land use and land Cover Survey Dynamically
The radar data used in the land use and land cover survey had got its extra advantages, especially in the dynamically surveying work. The AirSar, with the high spatial resolution, nearly 1m-3m, could be used to make the land use mapping. The scale of the map could reach to 1:10,000. The classification capabilities, which can match the second classes, could fulfil the standard of the state. The results of the thematic map could be used in the city and town planning, the land use planning or the other kinds of work. The investment of it is only one fourth compared with the photogrametric. If you think about the data collection and receiving easiness, who could refuse to use these “Hi-Tech” method in their work?
The spaceborne Sar data’s resolution could be chosen between 5m-50m, with compared more cheaper price. These kinds of data could meet the needs of 1:50,000 to 1:200,000 mapping work. Some special characteristics should be noted for RADARSAT data, that, with some different imaging mode could be selected, the data with different incident angle could contribute a lot to the classification of the land use especially in the crops distinguish.
The PANDA EYE EFFECT and land use survey. Last summer, we have an amazing discovery on the Radarsat data through the field work when we made the land use survey. we found that there are some very strange phenominon on the images: some small areas, the villages, were rounded by the dark circles, nearly every village had got this dark circle which much like the eyes of PANDA. These dark circles are damaged land which result from the bricks produced by the peasants. Based on the Radarsat data we can made the land use classification. The damaged land is more than that village areas, the rate reached to 1.2:1. We can not do these kind of work based on TM data. (see the attached images and classification map) The Wheat Growth Status Survey with Multi-Polar Sar Data
Although we have not got a chance to get the Multi-polar Sar data through the commercial channel at the present time, but the experimental study shows that these kind of data have got high potential in the Crops growth status surveying work. The result of the study and the classification map tell us the different level of the wheat growth. We hope that the RADARSAT-2 and Sir-C/X-SAR could do better jobs in near future.
The Other Crops Survey
The rice is one of the very important crops for Chinese people. The areas of the planting and the production of it are strictly related to the people’s life. The study results, through the multi-temporal data which achieved by the team of the RS Institute of Academy, China Agri. Univ. etc., led by Ms.Shao, has shown a bright prospects which is not to be thought about before.
How about the other kind of crops survey, for example Corn, Cotton and the others? It is perhaps a more difficult work compared with the rice survey because the difficulty in the work we are running has got a good preliminary result, the accuracy of the classification is about 85-90%.
The Fundamental Study
Although we have achieved a very good research results, but we have to say we must pay more attention to the fundamental study and research work.
The backscaterrametry work is a key link.
According to the Radar function:
The Index of the crop backscaterrametry s° could be gotten:
R = the dicetance between antina and the targets
Pr = the reflected signal power
Pt = the emission power by the device
A = equal area of the signal covered
Gt = emission antina multi-effect
Gr = receiving antina multi-effect
L = the system consums
s° = Index of backscaterrametry
In the above function, the only rate number Pr/Pt we must and could be measured besides the other factors, which could be defined by measurement or just instant elements.
And the very important thing is that the s°, which we could get through the measurements, is strong related to the grayness of the radar imageries. Certainly we must establish the relevant models. Through the analysis for the data from the measurements, we could get much important information about the relationship between the ground truth data and the radar images. According to this information or as the references for the case study work, we could understand the image better and process the remotely sensed data better.
The Conclusion and Foresee
It is very clear that the Radar remote sensing will play a very important role in the agricultural monitoring work, although we could not pay for the price of the data of the operational work at present. But we could pay future.
Perhaps at that time we will have to deal with hyper quantities, unbelievable cheap, real-time and any time, unaffected by the weather’s radar data in our surveying work. We have a lot of work to do before the days coming.
This kind of work, such as the mechanics of the imaging for the Radar systems, the interactive between the radar signals and the aims articles on the ground, the radar image processing and the information extractions so on.
We must also pay more attention to the application of the radar RS in the test areas and case studies. In these areas we could get a very meaningfully and sensitive results which could be used in big areas future.
Not only the tech. development but also the investment and the data price, the progress we have taken in the radar remote sensing development showed us a very bright prospects future. (Oct. 1999)