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

• US 9,046,363 B2
• Filed: 04/27/2012
• Issued: 06/02/2015
• Est. Priority Date: 04/27/2012
• Status: Active Grant

• Current Assignee: Eomap GmbH & Co. KG
• Original Assignee: Satop GmbH
• Inventors: Heege, Thomas
• Primary Examiner(s): Alsomiri, Isam
• Assistant Examiner(s): Abraham, Samantha K
• Application Number:
  US13/457,918
• Publication Number:
  US 20130286377A1
• Time in Patent Office: 1,131 Days
• Field of Search: 356/3.01, 356/4.01, 356/4.07, 356/5.01, 356/5.09, 356/9, 356/625
• US Class Current: 1/1
• 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 a first light intensity value indicative of a radiance at a first wavelength emanating from a surface area of a body of water at a first time;

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

calculating a plurality of modeled light intensity values at the first wavelength, wherein each of the plurality of modeled light intensity values is indicative of the radiance at the first wavelength emanating from the surface area of the body of water, and wherein each of the plurality of 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 a plurality of first differences between the first light intensity value and each of the plurality of modeled light intensity values;

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

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

displaying 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 plurality of first differences and the plurality of second differences, and wherein the estimated depth is displayed on a graphical user interface.

2. The method of claim 1, wherein the plurality of modeled light intensity values includes 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 seagrass.

3. The method of claim 1, wherein a contribution to the radiance caused by an adjacency of the surface area of the body of water to land has been removed from the first light intensity value.

4. The method of claim 1, wherein each of the plurality of modeled light intensity values also depends on a concentration of an assumed water constituent, and wherein the minimizing the deviation among the plurality of first differences and the plurality of second differences involves varying the concentration of the assumed water constituent.

5. The method of claim 4, wherein the assumed water constituent is taken from the group consisting of:

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

6. The method of claim 1, wherein the surface area corresponds to a pixel of a satellite image of the body of water, and wherein the estimated depth is indicated on the graphical user interface as a predetermined color of the pixel that corresponds to a range of the estimated depth.

7. A method comprising:

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

storing second light intensity values at the plurality of wavelengths each associated with the first 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 each associated with the first surface area of the body of water, wherein each of the modeled light intensity values depends on a reflectance of an assumed bottom cover on a bottom below the first surface area and on an assumed depth between the first surface area and the bottom;

determining a plurality of 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 plurality of differences by varying the assumed depth and the reflectance of the assumed bottom cover; and

displaying an estimated depth between the first surface area and the bottom, wherein the estimated depth is the assumed depth that results in the minimized sum of the plurality of differences, and wherein the estimated depth is displayed on a graphical user interface.

8. The method of claim 7, wherein the first light intensity values are taken from the group consisting of:

radiance values, reflectance values and irradiance values.

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 each of the modeled light intensity values depends on absorption by assumed water constituents between the first surface area and the bottom.

11. The method of claim 10, wherein the assumed water constituents are taken from the group consisting of:

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

12. The method of claim 7, wherein the first surface area corresponds to a pixel of a satellite image of the body of water.

13. A system for determining water depth, comprising:

a satellite database containing first light intensity values acquired over a plurality of wavelengths and second light intensity values acquired over the plurality of wavelengths, wherein the first light intensity values are acquired at a first time, and the second light intensity values are acquired at a second time, and wherein the first and second light intensity values are all associated with a defined surface area of a body of water;

a data analysis server that calculates modeled light intensity values at the plurality of wavelengths, wherein each of the modeled light intensity values is associated with the defined surface area and depends on a reflectance by an assumed bottom cover on a bottom below the defined surface area and on an assumed depth between the defined surface area and the bottom, wherein for each of the plurality of wavelengths the data analysis server determines a plurality of differences between the modeled light intensity values on the one hand and the first and second light intensity values on the other hand and minimizes a sum of the plurality of differences by varying the assumed depth and the reflectance of the assumed bottom cover; and

a graphical user interface on which an estimated depth between the defined surface area and the bottom is displayed, wherein the estimated depth is the assumed depth that results in the minimized sum of the plurality of differences.

14. The system of claim 13, wherein the sum of the plurality of differences is a sum of weighted differences that are weighted based on the corresponding wavelength.

15. The system of claim 13, wherein each of the modeled light intensity values depends on assumed water constituents between the first surface area and the bottom.

16. The system of claim 15, wherein the assumed water constituents are taken from the group consisting of:

suspended matter, phytoplankton, detritus and gelbstoff.

17. The system of claim 13, wherein the defined surface area corresponds to a pixel of a satellite image of the body of water.