Using multispectral satellite data to determine littoral water depths despite varying water turbidity

• US 9,613,422 B2
• Filed: 05/01/2015
• Issued: 04/04/2017
• Est. Priority Date: 04/27/2012
• Status: Active Grant

• Current Assignee: Eomap GmbH & Co. KG
• Original Assignee: Eomap GmbH & Co. KG
• Inventors: Heege, Thomas
• Primary Examiner(s): Ratcliffe, Luke
• Assistant Examiner(s): Abraham, Samantha K
• Application Number:
  US14/702,531
• Publication Number:
  US 20150310618A1
• Time in Patent Office: 704 Days
• CPC Class Codes: G01C 13/008 measuring depth of open water
• CPC Class Codes: G01S 11/14 using ultrasonic, sonic, or infrasonic waves
• CPC Class Codes: G01S 17/46 Indirect determination of position data
• CPC Class Codes: G06F 18/22 Matching criteria, e.g. proximity measures
• CPC Class Codes: G06T 7/50 Depth or shape recovery
• CPC Class Codes: G06V 10/58 relating to hyperspectral data
• CPC Class Codes: G06V 20/13 Satellite images
• CPC Class Codes: G06V 30/422 Technical drawings; Geographical maps
• CPC Class Codes: Y02A 90/30 Assessment of water resources

Abstract

Satellite data is used to determine water depth by accounting for the changing turbidity of the water over time and without requiring calibration using SONAR measurements. Radiance values at multiple wavelengths sensed at both a first time and a second time are stored in a database. Modeled reflectance values are calculated for a defined surface area on the water based on an assumed depth, assumed water constituents and assumed bottom cover. A plurality of differences between the modeled reflectance values and the reflectances sensed at the two times are calculated. A bathymetry application module minimizes the sum of the differences between the modeled and sensed subsurface reflectances by varying the assumed depth, bottom cover and water constituents. The differences are weighted based on wavelength before being summed. The depth that results in the minimized sum of the differences is the estimated depth, which is displayed on a graphical user interface.

Claims

1. A method comprising:

storing light intensity values acquired by an airborne sensor at a plurality of wavelengths each associated with a surface area on a body of water, wherein the body of water has a depth below the surface area; and

step for determining the depth using the light intensity values based on a first value indicative of turbidity below the surface area at a first time and on a second value indicative of turbidity below the surface area at a second time.

2. The method of claim 1, wherein the first value indicative of turbidity is taken from the group consisting of:

a concentration of particles below the surface area, an absorption of particles below the surface area, and a backscattering of particles below the surface area.

3. The method of claim 1, wherein the depth is determined without calibrating the determined depth using values acquired with SONAR.

4. The method of claim 1, further comprising:

removing from the light intensity values a contribution to the light intensity values caused by an adjacency of the surface area on the body of water to land.

5. The method of claim 1, wherein the surface area corresponds to a pixel of a satellite image of the body of water, further comprising:

indicating the depth on a graphical user interface as a predetermined color of the pixel that corresponds to a range that includes the depth.

6. The method of claim 1, wherein the light intensity values are taken from the group consisting of:

radiance values, reflectance values and irradiance values.

7. A method comprising:

storing a first value indicative of a light intensity at a wavelength emanating from a surface area of a body of water at a first time, wherein the light intensity is determined by a satellite sensor;

storing a second value indicative of the light intensity at the wavelength emanating from the surface area of the body of water at a second time;

calculating modeled light intensity values at the wavelength, wherein each of the modeled light intensity values is indicative of the light intensity at the wavelength emanating from the surface area of the body of water, and wherein each of the modeled light intensity values depends on an assumed bottom cover on a bottom below the surface area and on an assumed depth between the surface area and the bottom;

determining first differences between the first value and each of the modeled light intensity values;

determining second differences between the second value and each of the modeled light intensity values;

minimizing a deviation among the first differences and the second differences by varying the assumed depth and the assumed bottom cover; and

determining an estimated depth between the surface area and the bottom, wherein the estimated depth is the assumed depth that results in the minimized deviation among the first differences and the second differences.

8. The method of claim 7, wherein the first value indicates a light intensity taken from the group consisting of:

radiance, reflectance and irradiance.

9. The method of claim 7, wherein the assumed bottom cover is taken from the group consisting of:

sand, sea grass, rock, bottom sediment, and coral reef.

10. The method of claim 7, wherein the modeled light intensity values include a first modeled light intensity value based on the assumed bottom cover being sand and a second modeled light intensity value based on the assumed bottom cover being sea grass.

11. The method of claim 7, wherein each of the modeled light intensity values also depends on an absorption by assumed water constituents between the surface area and the bottom.

12. The method of claim 11, wherein the assumed water constituents are taken from the group consisting of:

suspended inorganic matter, phytoplankton, macrophytes, and dissolved organic matter.

13. The method of claim 11, wherein the surface area corresponds to a pixel of a satellite image of the body of water.

14. A method comprising:

storing first light intensity values at a plurality of wavelengths each associated with a surface area of a body of water, wherein each of the first light intensity values is acquired at a first time by a satellite sensor;

storing second light intensity values at the plurality of wavelengths each associated with the surface area of the body of water, wherein each of the second light intensity values is acquired at a second time;

calculating modeled light intensity values at the plurality of wavelengths, wherein each of the modeled light intensity values depends on an assumed bottom cover on a bottom below the surface area and on an assumed depth between the surface area and the bottom;

determining differences between the modeled light intensity values on the one hand and the first and second light intensity values on the other hand for each of the plurality of wavelengths;

minimizing a sum of the differences by varying the assumed depth and the assumed bottom cover; and

determining an estimated depth between the surface area and the bottom, wherein the estimated depth is the assumed depth that results in the minimized sum of the differences.

15. The method of claim 14, wherein the sum of the differences is a sum of weighted differences that are weighted based on the corresponding wavelength.

16. The method of claim 14, wherein each of the modeled light intensity values also depends on assumed water constituents between the surface area and the bottom.

17. The method of claim 16, wherein the assumed water constituents are taken from the group consisting of:

suspended matter, phytoplankton, detritus and gelbstoff.

18. The method of claim 14, wherein the surface area corresponds to a pixel of a satellite image of the body of water.

19. The method of claim 14, wherein the estimated depth is determined without using values acquired with SONAR.

20. The method of claim 14, wherein the second time is more than a day after the first time.