Twenty-five pixel averages of the DN values (an 8 bit, unsigned integer for each pixel in the SAR image) of a representative location on the crater floor (dni) and a location in the terrain surrounding the crater (dno). A representative location in the crater floor is similar in brightness to the majority of the crater floor. A representative location in the terrain surrounding the crater is a piece of terrain near the crater that is similar in character to the terrain that the crater formed on but that is unaffected by the crater. Within the crater we chose a piece of floor that appeared to be similar in brightness to the majority of the floor material. The difference between these values (dnd) gives an estimate of the relative radar brightness of the crater interior. Individual DN values can be converted to radar cross section in decibels by the formula:
One DN equals 0.2 dB of radar backscatter.
The average DN is the average of the logaritm of the backscatter at each pixel location. This calculation was only made for craters > 16 km in diameter.