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Agriculture
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A study on single and multiple polarization SAR image interpretation for agri-application
Zhang Wei, Yan Tailai
Beijing Agricultural University
Remote Sensing Center
Beijing 100094, China
Abstract
The imaging mechanics of SAR is very different from the other remote sensing system. It has got its own character. In this paper for the aim of agriculture Remote Sensing application, introduce the characters of the vegetations, soil, road interpretation and the measurement method of some articles in SAR image, and interpretation physics concept. As a comparison, introduce the interpretation characters, image processing and mapping of multi-polarization SAR image.
A. Background
Radar-system makes photos based on the reflection power of Radar emitted from its antenna, polarization direction and the phase-shift. This is one of the fundamental point of Radar Remote Sensing which is different from the other Remote Sensing system. We can select the depression angle, frequency, polarization direction, emitting power, modulation modle, and also select the receiving modle, i.e., polarization direction of reflection Radar wave, and threshold of reflection power. Therefore, man’s initiative of radar Remote Sensing is greater than other Remote Sensing systems on the respect of obtaining the information of ground. The distinguishing teach. features of radar include the following.
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All-weather and all-day-long time monitoring. Especially, this point is very important for the agricultural application, for example the crops yielding estimation, the disaster survey and the other monitoring work. This feature has been known for many people today.
- The resolution of radar Remote Sensing image is independent upon the solid-angle of object, but dependent upon the width of modulating pulse of radar. That is why the resolution of radar Remote Sensing image is independent upon the altitude of the sensor-carrier. At the very high altitude, the sensor of radar is able to identify the small object such as rail, steel tube, drainage ditch, even flying locust.
- Radar has the ability to penetrate ground. The wave penetrating the leaves of crops, so we can obtain the information of soil moisture under the leaves of crops. In L band, radar can penetrate the dry sand as deep as 20 meters.
- Using the effection of special reflection we can obtain the information of special objects, such as steel struction, water body, building etc.
- Based on the effection of two-specular-reflection or three-specular-reflection, radar is sensitive to the altitude change of object at small area, we can measure the height of sea
wave, river bank, etc.
- Some special object such as some rocks, we soil, etc, they can affect the polarization direction of radar. If we can receive the cross-polarization radar image, we will identify the objects.
Generally speaking, the image of radar Remote Sensing has got more information per unit area than ones of the other Remote Sensing system. We are able to obtain the information which is not able to abtain from the other Remote Sensing systems. Perhaps, this is why the radar Remote Sensing has taken a big progress in the past few years. And now, ERS-1, JERS-1 and ALMAZ have been launched, some more radar sat will be launched by the countries include China. In this case, one of the important problems is how to cultivate the radar data for the applications especially for the agricultural aim.
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