This deals with the different types of imaging sensors, its constituents, thermal control systems, satellite communication, sensor detector assemblies, sensor design.

1. INFRA-RED IMAGING
SENSORS AND INSTRUMENTS
ON GEO STATIONARY
SATELLITES
AASHEESH TANDON AND PRIYANKA GOSWAMI
INSTITUTE OF TECHNOLOGY
NIRMA UNIVERSITY

2. 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 includeWeather Prediction, Global climate studies,
Cyclone monitoring and warning, Earth resource studies, detection of
forest fires, and many more applications

3. 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

4. IR IMAGING SENSOR TYPES
A. 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

5. IR IMAGING SENSOR TYPES
B. 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.

6. CONSTITUENTS OF A SATELLITE IR IMAGING
SENSOR
A.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

7. CONSTITUENTS OF A SATELLITE IR IMAGING
SENSOR
B. 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

8. CONSTITUENTS OF A SATELLITE IR IMAGING
SENSOR
C. Electronic IR Detectors and Cryogenic coolers
• There are two basic types of photon (radiative energy)
detectors:
1. Majority (electron): detector is photoconductive
2. 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 ElectronicWork Function law.
• The detector elements have to be operated at the lowest
possible cryogenic temperatures to obtain meaningful
electronic signal

9. 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

10. 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

11. 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.

12. SENSOR DETECTOR ASSEMBLY (CASE STUDY)
A.Visible Infrared Imaging Radiometer Suite (VIIRS) [Raytheon]
• Inspecting radiometer – accumulatesVisible 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, andTIR energy.

13. 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.

14. Thermal Infrared
Sensor (TIRS) Assembly

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

16. THANK YOU !