How does pixel size or instantaneous field of view relate to the size of objects can actually be distinguished in a space photograph?
Even though people often say that TM “resolution” is 30 m, that is actually technically incorrect. For Landsat TM, pixel size or instantaneous field of view (IFOV) is what is actually 30 m x 30 m. This number does not mean that objects of 30 m in width can be identified in an image. The ability of the system to image objects of various widths depends on a number of factors i ncluding the contrast between the objects. A more inclusive and realistic (but also subjective) measure of resolution used primarily in aerial photography is ground resolved distance (GRD). Instead of specifying a resolution for an entire system, you can also think about resolution from an image-specific point of view. In general every image has a ground resolved distance (GRD) that depends on spatial resolution, contrast and texture as well as on the characteristics of the system that was used to capture the image. As an example, image a winter scene and a summer scene of a nothern decisuous forest with clearcut a