Soil and topography surveying

1. A method of characterizing subsurface conditions in a selected geographic region previously surveyed to identify discrete zones within the region corresponding to a reference soil series having an associated description of soil layers corresponding to the soil series and soil properties common to each layer, the method comprising

selecting a test position in each identified zone;

deploying a sensing tool at the selected position within the geographic region, the tool constructed to be responsive to a selected subsurface material attribute; and

determining, from a signal received from the deployed tool, a subsurface material characteristic at multiple, discrete depths corresponding to layer positions described in the reference soil series description.

2. The method of claim 1 further comprising comparing the determined subsurface material characteristic to soil layer properties listed in the reference soil series description.

3. The method of claim 1 wherein the discrete zones correspond to individual Soil Map Units as outlined on an USDA-NRCS Soil Survey map, and wherein the multiple, discrete depths correspond to layers described in the description of the reference soil series of the Soil Map Unit associated with the identified zone.

4. The method of claim 1 further comprising comparing the determined subsurface material characteristic to a subsurface material characteristic reference profile associated with the geographic region to determine a correlation between the subsurface material characteristic reference profile and the subsurface material characteristic as determined from the signal received from the deployed tool.

5. The method of claim 4 wherein comparing the determined subsurface material characteristic to the subsurface material reference characteristic profile associated with the geographic region includes comparing soil texture at a selected depth, as determined from the determined subsurface material characteristic, with a reference texture as determined from the subsurface material reference characteristic profile.

6. The method of claim 4 wherein the subsurface material characteristic profile comprises a digital log of a soil property as a function of depth.

7. The method of claim 1 wherein deploying the tool includes penetrating soil with the tool.

8. The method of claim 7 wherein the soil is penetrated to a depth of at least 24 inches.

9. The method of claim 1 wherein the subsurface material characteristic comprises a log of data taken at multiple depths at the selected position.

10. The method of claim 1 wherein the tool is responsive to light reflected from adjacent subsurface material in situ, and wherein determining the subsurface material characteristic includes generating a depth-referenced, rastered image of the subsurface material.

11. The method of claim 1 further comprising

traversing the geographic region while obtaining landscape position and elevation measurements;

combining the position and elevation measurements to form a digital elevation model;

adjusting a depth reference of the subsurface material characteristic determined at each of several test locations in accordance with the digital elevation model; and then

combining the depth reference-adjusted subsurface material characteristics to form a three-dimensional subsurface model of the material characteristic.