Classification of matter from space
Multiple synthetic aperture radar “SAR” images of a target area on the earth are acquired using a satellite travelling in an orbit above the earth in a single pass of the satellite over the target area. In some methods, the data for each image is acquired from a different angle of incidence with respect to the target area. Then, the variation of quantity of backscattered radiation with respect to angle of incidence is analysed and used to identify matter imaged in a pixel or pixel group. In other methods, the data for each image is acquired from a different angle of incidence with respect to the target area, and the different angles of incidence are determined based on the specular reflection curve for a particular material. Then the quantity of backscattered radiation is analysed to determine whether the particular material is present based on the quantity of backscattered radiation. ‘Extended dwell spotlight acquisition’ geometry may be used in which image data acquisition apparatus may be locked to illuminate same target as the satellite passes over the target for a period of for example 20 seconds.
1. A method of earth observation comprising:
acquiring multiple synthetic aperture radar “SAR” images of a target area on the earth using a satellite travelling in a low earth orbit above the earth, wherein the data for each image is acquired from a different angle of incidence with respect to the target area and the different angles of incidence are 10° or more, wherein the acquiring comprises controlling an orientation of image acquisition apparatus on the satellite with respect to the target area to remain directed at the target area for a predetermined period as the satellite passes over the target area whereby to acquire the multiple images in a single pass of the satellite over the target area, the controlling the orientation of the image acquisition apparatus with respect to the target is achieved by controlling the orientation of the satellite with respect to the target area, and at least one of the different angles of incidence is generated forward and/or backward along a flight track of the satellite;
for at least one pixel or pixel group in the images, analysing a variation of quantity of backscattered radiation with respect to angle of incidence; and
using the analysis to identify matter imaged in the pixel or pixel group.
2. The method of claim 1 , wherein the different angles of incidence are determined based on a specular reflection curve for particular matter.
3. The method of claim 2 , wherein the particular matter is water.
4. The method of claim 1 , comprising acquiring image data during discrete intervals within the predetermined period.
5. The method of claim 4 , comprising controlling the orientation of the image acquisition apparatus to enable the acquisition of image data from a continuous range of different angular positions with respect to the target during the discrete intervals within the predetermined period.
6. The method of claim 1 , wherein the analysing comprises allocating at least two subsets of the angles of incidence to respective channels and summing pixel intensity values to calculate an intensity value for each channel.
7. The method of claim 6 , comprising representing the summed intensity values on a visual display.
8. The method of claim 6 , comprising allocating a subset of the different angles of incidence to each of primary colours for a visual display and using the summed intensity values to generate a colour representation of the target area.
9. The method of claim 1 , wherein at least some of the incidence angles are generated backward along the flight track of the satellite.
10. A non-transitory computer readable data storage comprising instructions which when implemented on one or more processors on a satellite cause the implementation of a method of earth observation, the method comprising:
acquiring multiple synthetic aperture radar “SAR” images of a target area on the earth using a satellite travelling in a low earth orbit above the earth, wherein the data for each image is acquired from a different angle of incidence with respect to the target area and the different angles of incidence are 10° or more, wherein the acquiring comprises controlling an orientation of image acquisition apparatus on the satellite with respect to the target area to remain directed at the target area for a predetermined period as the satellite passes over the target area whereby to acquire the multiple images in a single pass of the satellite over the target area, the controlling the orientation of the image acquisition apparatus with respect to the target is achieved by controlling the orientation of the satellite with respect to the target area, and at least one of the different angles of incidence is generated forward and/or backward along a flight track of the satellite;
for at least one pixel or pixel group in the images, analysing a variation of quantity of backscattered radiation with respect to angle of incidence; and
using the analysis to identify matter imaged in the pixel or pixel group.