3. Resolution

Radiometric resolution

The radiometric resolution specifies how well the differences in brightness in an image can be perceived; this is measured through the number of the grey value levels. The maximum number of values is defined by the number of bits (binary numbers). An 8 bit representation has 256 grey values, a 16 bit (ERS satellites) representation 65.536 grey values.

The finer or the higher the radiometric resolution is, the better small differences in reflected or emitted radiation can be measured, and the larger the volume of measured data will be (compare with the image on the right).

The advantage of a higher radiometric resolution is rather small - when comparing LANDSAT-MSS (6 bits) and TM (8 bits) the improvement is in the order of 2-3%.

Radiometric resolution depends on the wavelengths and the type of the spectrometer:

• LANDSAT-MSS (from LANDSAT 1-3): 6 bits (64 grey values)
• IRS-LISS I-III: 7 bits (128 grey values)
• LANDSAT-TM (from LANDSAT 4-5) & SPOT-HRV: 8 bits (256 grey values)
• LANDSAT-ETM & ETM+ (from LANDSAT 6-7): 9 bits (only 8 bits are transmitted)
• IRS-LISS IV: 10 bits (only 7 bits are transmitted)
• IKONOS & QuickBird: 11 bits.