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
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
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.