IRS-1C User's Handbook

LISS-III Camera

Optics and electronics

LISS-III operates in four spectral bands. There is a separate optics and detector array for each band. Three bands (B2, B3 and B4) are in the visible and near infrared region. B5 is in short wave infrared region. Since the first three bands of LISS-III are in the same spectral region as IRS-1A/1B/P2 sensors, the same nomenclature is continued. Bands B2, B3 and B4 of IRS-1C are therefore identical to that of IRS-1A/1B/P2.

The camera uses refractive optics. The collecting optics consists of eight refractive lens elements with interference filter in front. A linear array of 6000 elements of CCDs is used for visible and infrared bands. It has a pixel size of 10 micron by 7 micron. It has separate readouts for odd and even pixels on two channels. Each detector has its own detector drive electronics. Band 2, 3 and 4 have separate video chains. Band 5 consists of a 2100 element linear CCD array (7 modules of 300 pixels) with a pixel size of 30 micron by 30 micron. Odd and even pixels are staggered by 52 microns in the along track direction. The device will be operated at -10 deg C or at -5 deg C with a temperature stability of ±0.1 deg C. Four independently selectable gains are provided for each band of LISS-III.

LISS-III camera

Inflight calibration

The inflight calibration of the camera is carried out using LEDs. Six Non zero exposure levels spanning the dynamic range are provided for each detector. Four LEDs are used for illumination. Two LEDs operate at a time to cover half the length of CCD. The LEDs are operated in pulsed mode and the duration during which the LEDs are 'ON' is varied in specific steps. Each LED has a cylindrical lens to maximize the intensity. For Band 5, the LEDs have very small angular divergence. The CCD detector integrates the light falling on it during one readout period. A calibration cycle comprises of 2048 lines. The time taken for one calibration cycle of LISS-III is 7.3 seconds. The Band 5 calibration data is multiplexed with data of other bands.