Changes in this quantity are associated with changes in radar reflectivity in a form of interferometry whose control variables are “persistent scatterers.” Measurements of this quantity standardized to the GTOPO30 (“G-topo-thirty”) system have since been improved by the ASTER instrument. Techniques like IfSAR (“IF-sar”) and InSAR (“IN-sar”) are used to obtain image representations (-5[1])of this quantity called DEMs (“D-E-M’s”). Temperature gradients relative to this quantity in dry and moist air parcels define the adiabatic lapse rate. (10[1])High values of latitude and this quantity form the “tree line” of a habitat. (10[1]-5[1])Constant (10[1])values of this quantity (10[1])are represented by contour lines (10[2])on (10[1])topographic (10[1])maps. (10[1])For 10 points, what quantity (10[1])is defined as zero at sea level? ■END■