Apparatus for and method of forest-inventory management

A system for creating an enhanced digital terrain model having enhanced resolution and accuracy for a target portion of the surface of the Earth, the target portion being subdivided into sub-portions of a first size, and being further subdivided into sub-portions of a second size, the second size being smaller than the first size, the system comprising:

• a. an electronic interface for receiving, and a non-transitory memory for storing:
• i. a base digital terrain model specifying an elevation for each first size sub-portion, the base digital terrain model being based on interferometric synthetic aperture radar data;
• ii. a calibration digital terrain model corresponding to a reference portion of the target portion specifying a reference elevation for each second size sub-portion;
• b. a computer processor configured to:
• i. for the reference portion, calculate errors in the digital terrain model by comparing the elevations in the digital terrain model with the reference elevations in the calibration digital terrain model for the reference portion;
• ii. obtain stereo imagery from an airborne or spaceborne imaging sensor of the target portion, the imagery being sufficient to permit the calculation of a surface elevation of each second size sub-portion;
• iii. calculate a digital surface model by stereophotogrammetric analysis of the imagery, the digital surface model specifying a surface elevation for each second size sub-portion;
• iv. calculate for each second size sub-portion, from the digital surface model, a terrain curvature value based on the digital surface model;
• v. calculate a terrain curvature error correction function by comparing the errors in the digital terrain model with the terrain curvature values for the reference portion, the terrain curvature error correction function estimating the error in the digital terrain model elevations as a function of terrain curvature value;
• vi. calculate, for each second size sub-portion, a corrected elevation by applying the terrain curvature error correction function to the elevation of the corresponding first size sub-portion in the digital terrain model based on the terrain curvature value of the second size sub-portion to produce the corrected elevation for the second size sub-portion in the enhanced digital terrain model;
• and
• vii. produce a digital image of the target portion, the digital image comprising pixels, each pixel having a pixel size of at most the second size, each pixel corresponding to one second size sub-portion of the target portion, each pixel having a value calculated based on the corrected elevation specified in the enhanced digital terrain model for the second size sub-portion corresponding to the pixel, wherein the value is calculated in a manner to distinguish sub-portions of the target area at differing elevations from each other.