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 |
| flooding |
3-5 hours |
| drought |
15 days |
agri. sustain develp:
(resources sustainable use) |
1-2 year |
| agri. environment survey |
3-6 mons . |
The Effectiveness analysis for the TM data
(Beijing Ground Receiving Station)
Crp.Grw.Ssn.
| No. |
Area |
P/R |
peiod |
Scens |
No Cld.Scn |
Effect |
| 1. |
Beijing |
123-32 |
1993-1994 |
37 |
1(Mar-Oct) |
3%. |
| 2. |
Wuxi |
119-30 |
1986-1995 |
102 |
1(Mar-Oct) |
1%. |
| 3. |
Penglai |
120-34 |
1986-1995 |
104 |
3(Mar-Oct) |
5%. |
| 4. |
Changch |
118-30 |
1986-1996 |
116 |
6(May-Sep) |
5%. |
| 5. |
Dengko |
129-32 |
1986-1996 |
129 |
5(May-Sep) |
3%. |
| 6. |
Changsha |
123-40 |
1987-1996 |
112 |
5(Mar-Oct) |
6%. |
| 7. |
Zhaoqing |
129-44 |
1986-1996 |
106 |
1(Mar-Oct) |
1%. |
| 8. |
Hami |
138-30 |
1994-1996 |
35 |
2(Apr-Sep) |
6%. |
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)
