Method and system for classifying a terrain type in an area

1. A method for classifying a terrain type in an area, the method comprising the steps of:

obtaining a plurality of overlapping aerial images of the area, wherein the plurality of overlapping aerial images are not images that only differ by a wavelength band that each aerial image out of the plurality of overlapping aerial images uses:

calculating at least one terrain type index for each part of each of the aerial images which lies in the area, where the at least one terrain type index represents the terrain type;

determining at least one effective terrain type index for each part of the area based on the calculated at least one terrain type index for the corresponding part of each of the overlapping aerial images, the effective terrain type index for each part of the area being determined via taking either a statistical average or a weighted statistical average of corresponding terrain type indices from each corresponding part of each of the overlapping aerial images, which correspond to this part of the area: and

classifying the parts of the area for which at least one predetermined conditions is met as containing the terrain type, wherein at least one of the at least one predetermined condition relates to a value of the determined at least one effective terrain type index.

2. The method according to claim 1 , where the classified terrain type is water and where the at least one terrain type index comprises a water index.

3. The method according to claim 1 , wherein surface elevation data is used at least one of to relate the images in the obtained plurality of overlapping aerial images to area data or to relate the effective terrain type index to area data.

4. The method according to claim 1 , wherein the overlapping aerial images are images taken from at least one satellite.

5. The method according to claim 1 , further comprising a step of calibrating said plurality of aerial images of an area for at least one wavelength band and preferably for all wavelength bands which are used for calculating the at least one terrain type index.

6. The method according to claim 1 , further comprising a step of calibrating said plurality of aerial images of an area for all wavelength bands which are used for calculating the at least one terrain type index.

7. The method according to claim 1 , wherein the step of determining the at least one effective terrain type index for each part of the area comprises using at least one of a voting mechanism or a statistical method.

8. The method according to claim 1 , wherein the method is used to classify a plurality of terrain types based on a plurality of terrain type indices each representing a specific terrain type.

9. The method according to claim 1 , further comprising a step of obtaining surface elevation data of the area, and where the at least one pre-determined condition also relates to surface elevation data for the corresponding part of the area.

10. The method according to claim 1 , further comprising a step of obtaining at least one shadow mask.

11. The method according to claim 10 , wherein the step of obtaining said at least one shadow mask comprises the steps of:

obtaining for each of the images in the plurality of overlapping aerial images information relating to the position of the sun at the time the image was taken and information relating to the angle from which the image was taken;

providing a three-dimensional model of the area;

determine the position of the shadow in each of the images in the plurality of overlapping aerial images based on the provided three-dimensional model of the area, based on the information relating to the position of the sun at the time the image was taken and based on the information relating to the angle from which the image was taken.

12. The method according to claim 10 , wherein said terrain type index is only calculated for the parts of each of the images in the plurality of overlapping aerial images for which no shadow has been determined.

13. The method according to claim 10 , wherein said terrain type index is only used for the parts of each of the images in the plurality of overlapping aerial images for which no shadow has been determined.

14. A computer program comprising at least one non-transitory computer-readable storage medium having computer-readable program code for classifying a terrain type in an area embodied therein, the computer-readable program code being configured to execute the steps of:

obtaining a plurality of overlapping aerial images of the area, wherein the plurality of overlapping aerial images are not images that only differ by a wavelength band that each aerial image out of the plurality of overlapping aerial images uses:

calculating at least one terrain type index for each part of each of the aerial images which lies in the area, where the at least one terrain type index represents the terrain type;

determining at least one effective terrain type index for each part of the area based on the calculated at least one terrain type index for the corresponding part of each of the overlapping aerial images, the effective terrain type index for each part of the area being determined via taking either a statistical average or a weighted statistical average of corresponding terrain type indices from each corresponding part of each of the overlapping aerial images, which correspond to this part of the area: and

classifying the parts of the area for which at least one predetermined conditions is met as containing the terrain type, wherein at least one of the at least one predetermined condition relates to a value of the determined at least one effective terrain type index.

15. A system for classifying a terrain type in an area, the system comprising:

one or more memory storage areas configured to store a plurality of overlapping aerial images of the area, wherein the plurality of overlapping aerial images are not images that only differ by a wavelength band that each aerial image out of the plurality of overlapping aerial images uses:

calculate at least one terrain type index for each part of each of the aerial images which lies in the area, where the at least one terrain type index represents the terrain type;

determine at least one effective terrain type index for each part of the area based on the calculated at least one terrain type index for the corresponding part of each of the overlapping aerial images, the effective terrain type index for each part of the area being determined via taking either a statistical average or a weighted statistical average of corresponding terrain type indices from each corresponding part of each of the overlapping aerial images, which correspond to this part of the area: and

classify the parts of the area for which at least one predetermined conditions is met as containing the terrain type, wherein at least one of the at least one predetermined condition relates to a value of the determined at least one effective terrain type index.

16. The system according to claim 15 , wherein the processing unit further is configured to calibrate said plurality of aerial images of an area for at least one wavelength band used for calculating the at least one terrain type index.

17. The system according to claim 15 , wherein the processing unit further is configured to calibrate said plurality of aerial images of an area for all wavelength bands used for calculating the at least one terrain type index.

18. The system according to claim 15 , wherein the processing unit further is configured to obtain at least one shadow mask.

19. The system according to claim 15 , wherein:

surface elevation data of the area is attributed to the plurality of overlapping aerial images of the area, and

the at least one pre-determined condition also relates to surface elevation data for the corresponding part of the area.