A STUDY OF INFRA-RED IMAGING SENSORS AND INSTRUMENTS ON GEO-STATIONARY SATELLITES

INFRA-RED IMAGING SENSORS AND

INSTRUMENTS ON GEO STATIONARY SATELLITES

AASHEESH TANDON AND PRIYANKA GOSWAMI

INSTITUTE OF TECHNOLOGYNIRMA UNIVERSITY

INTRODUCTION• Infrared (IR) Imaging from Satellites is an advanced field

of space science and technology• The first satellite with thermal imaging capability was by

NOAA/NASA in 1970’s• Images are generated by emitted IR radiation from the

Earth surface• Satellite Thermal imaging systems exploit MWIR (3-5um)

and LWIR (8-14um)• Applications include Weather Prediction, Global climate

studies, Cyclone monitoring and warning, Earth resource studies, detection of forest fires, and many more applications

GEOSTATIONARY SATELLITES (GEO-S) FOR IR IMAGING• GEO-S placed in geostationary Earth orbit

or geosynchronous equatorial orbit (GEO) circular orbit 35,786 kilometers above the Earth's equator and following the direction of the Earth's rotation• GEO-S Imaging sensors can see 1/3 of the earth sphere

only, centered with the satellite location• USA, Europe, India, Japan, China have deployed

operational GEO-S for earth imaging, mainly for meteorological applications

IR IMAGING SENSOR TYPESA. Imager/Radiometer

• Imagers provide images for the entire Earth disc or a part of it.

• They have much wider bands, and fewer imaging channels

• Resolutions are 500mts-2.5km• Imaging intervals can be 1min to 20 min.• Generally 48 or more images can be generated and

transmitted per day

IR IMAGING SENSOR TYPESB. Sounder

• Special type of multi band IR sensor.• Related with emission or absorption of EM/IR

radiation of atmospheric water vapor, CO2, Ozone. • Sounder instruments have resolutions of 4-10km• Provide up to 6-8 images per day.

CONSTITUENTS OF A SATELLITE IR IMAGING SENSORA. Telescope and Scanning systems

• Telescope configuration: Cassegrain or RC type• Focal length that covers the Earth disc and its

surrounding space • The primary mirror can be “scooped” to make it light-

weighted• “Scan Mirror” is required to be placed before the

telescope

CONSTITUENTS OF A SATELLITE IR IMAGING SENSORB. Pre – detector optical system

• Several IR imaging detectors are required to cover the different IR bands, to provide the images of features on Earth• “Beam splitters” are placed, to only transmit that part of

the IR radiation required for a specific detector• e.g. Gold di-chorics are used with different thickness to

split 8-14um bands and glass filters are also used for 2.5-14 um radiation bands

CONSTITUENTS OF A SATELLITE IR IMAGING SENSORC. Electronic IR Detectors and Cryogenic coolers • There are two basic types of photon (radiative energy)

detectors:1. Majority (electron): detector is photoconductive2. Minority (hole): detector is both photoconductive and

photovoltaic• Most GEO satellites with IR imaging use cryogenic

cooled HgCdTe (photoconductive) detector• IR detectors being photoconductive, the

performance is governed by Planck’s radiation law, Stephan-Boltzzman black body law, and Electronic Work Function law.

• The detector elements have to be operated at the lowest possible cryogenic temperatures to obtain meaningful electronic signal

THERMAL CONTROL SYSTEM • This system is cardinal to achieve optimum

performance and it ensures efficient equipment operation

• The generated heat is transferred by TCS from the spacecraft or space station to the space.

• The TCS system has two subsystems – a Passive Thermal Control System (PTCS) and an Active Thermal Control System (ATCS).

• The cooling mechanism in GEO satellites can be of two types:1. Active, using cryogenic electro-mechanical coolers (sterling

cycle)2. Passive, using radiant cooler

SATELLITE COMMUNICATION

• Line of Sight Communication

• Uplink Station on ground -> Signal Processing -> Data Transmission -> Modified Signal Received at the Satellite -> Signal Processing -> Retransmission of Signal back to Earth -> Ground Equipment Receives the Signal

DATA TRANSMISSION• Analog Signal from Sensor -> Pre-processing ->

ADC -> Serial Stream of Data -> Modulation -> Transmission to Earth

• Data Processing Software Solutions: TeraScan, Geomatica, Idrisi, GRASS GIS

• Different product services include data acquisition, sensor conversion, visualization, algorithm generation, data export, environmental monitoring, data cataloguing, etc.

SENSOR DETECTOR ASSEMBLY (CASE STUDY)A. Visible Infrared Imaging Radiometer Suite (VIIRS) [Raytheon]

• Inspecting radiometer – accumulates Visible and IR imagery, and radiometric measurements of land, atmosphere, oceans and, cryosphere.

• 22 band optomechanical radiometer - uses a cross track rotating telescope fore optics design.

• Spectral range from 0.41 to 12.5 microns. • The observation scene is imaged onto 3 focal planes,

splitting the VNIR, SWIR, MWIR, and TIR energy.

SENSOR DETECTOR ASSEMBLY (CASE STUDY)B. Thermal Infrared Sensor (TIRS) • Mounted on in the Landsat 8 [formerly LDCM]

mission by NASA• Collects image data over a 185 km swath for two

narrow spectral thermal bands with 100 meters resolution.

• A push broom type sensor – Uses focal plane with long arrays of photo-sensitive detectors.

• A refractive telescope having four elements and focuses a f/1.6 beam of thermal radiation onto a cooled focal plane.

• Two sate cryocooler is employed to let detectors function at the required temperature of 43K.

Thermal Infrared Sensor (TIRS) Assembly

SENSOR DESIGN

Building blocks of the design criterion are - Phenomenology, FPA characteristics, Design operation range performance etc.

THANK YOU !