Module 1: Introduction and Concepts of Remote Sensing
Module 2: Sensors, Platforms and Tracking System
Module 3: Fundamentals of Aerial Photography
Module 4: Digital Image Processing
Module 5: Microwave and Radar System
Module 6: Geographic Information Systems (GIS)
Module 7: Data Models and Structures
Module 8: Map Projections and Datum
Module 9: Operations on Spatial Data
Module 10: Fundamentals of Global Positioning System
Module 11: Applications of Remote Sensing for Eart...
Lesson 6 Remote Sensing Platforms
6.1 What is a Platform?
For remote sensing applications, sensors should be mounted on suitable stable platforms. These platforms can be ground based air borne or space borne based. As the platform height increases the spatial resolution and observational area increases. Thus, higher the sensor is mounted; larger the spatial resolution and synoptic view is obtained. The types or characteristics of platform depend on the type of sensor to be attached and its application. Depending on task, platform can vary from ladder to satellite. For some task sensors are also placed on ground platforms. Though aircrafts and satellites are commonly used platforms, balloons and rockets are also used.
Brief descriptions of these platforms are given in subsequent sections.
6.2 Type of Platforms
Three types of platforms are used to mount the remote sensors –
Ground Observation Platform
Airborne Observation Platform, and
Space-Borne Observation Platform
6.2.1 Ground Observation Platform
Ground observation platforms are used to record detailed information about the objects or features of the earth’s surface. These are developed for the scientific understanding on the signal-object and signal-sensor interactions. Ground observation includes both the laboratory and field study, used for both in designing sensors and identification and characterization of land features. Ground observation platforms include – handheld platform, cherry picker, towers, portable masts and vehicles etc. Portable handheld photographic cameras and spectroradiometers are largely used in laboratory and field experiments as a reference data and ground truth verification.
6.2.2 Air Borne Based Platform
Airborne platforms were the sole non-ground-based platforms for early remote sensing work. Aircraft remote sensing system may also be referred to as sub-orbital or airborne, or aerial remote sensing system. At present, airplanes are the most common airborne platform. Other airborne observation platforms include balloons, drones (short sky spy) and high altitude sounding rockets. Helicopters are occasionally used.
188.8.131.52 Balloon Platform
Balloons are used for remote sensing observation (aerial photography) and nature conservation studies. The first aerial images were acquired with a camera carried aloft by a balloon in 1859. Balloon floats at a constant height of about 30 km. It consists of a rigid circular base plate for supporting the entire sensor system which is protected by an insulating and shock proof light casing. The payload used for Indian balloon experiment of three Hasselblad cameras with different film filter combinations, to provide PAN, infra red black and white and infra red false color images. Flight altitude being high compared to normal aircraft height used for aerial survey, balloon imagery gives larger synoptic views. The balloon is governed by the wind at the floating altitude. Balloons are rarely used today because they are not very stable and the course of flight is not always predictable, although small balloons carrying expendable probes are still used for some meteorological research.
Drone is a miniature remotely piloted aircraft. It is designed to fulfill requirements for a low cost platform, with long endurance, moderate payload capacity and capability to operate without a runway or small runway. Drone includes equipment of photography, infrared detection, radar observation and TV surveillance. It uses satellite communication link. An onboard computer controls the payload and stores data from different sensors and instruments. The payload computer utilizes a GSM/GPRS (where available) or independent satellite downlink, and can be monitored its position and payload status from anywhere in the world connected to the internet.
Drone was developed in Britain during World War-II, is the short sky spy which was originally conceived as a military reconnaissance. Now it plays important role in remote sensing. The unique advantage is that it could be accurately located above the area for which data was required and capable to provide both night and day data.
Special aircraft with cameras and sensors on vibration less platforms are traditionally used to acquire aerial photographs and images of land surface features. While low altitude aerial photography results in large scale images providing detailed information on the terrain, the high altitude smaller scale images offer advantage to cover a larger study area with low spatial resolution.
The National High Altitude Photography (NHAP) program (1978), coordinated by the US Geological Survey, started to acquire coverage of the United States with a uniform scale and format. Beside aerial photography multi spectral, hyperspectral and microwave imaging is also carried out by aircraft; thereafter multi spectral, hyperspectral and microwave imaging were also initiated.
Aircraft platforms offer an economical method of remote sensing data collection for small to large study areas with cameras, electronic imagers, across- track and along-track scanners, and radar and microwave scanners. AVIRIS hyperspectral imaging is famous aircraft aerial photographic operation of USGS.
184.108.40.206 High Altitude Sounding Rockets
High altitude sounding rocket platforms are useful in assessing the reliability of the remote sensing techniques as regards their dependence on the distance from the target is concerned. Balloons have a maximum altitude of approximately 37 km, while satellites cannot orbit below 120 km. High altitude sounding rockets can be used to a moderate altitude above terrain. Imageries with moderate synoptic view can be obtained from such rockets for areas of some 500,000 square kilometers per frame. The high altitude sounding rocket is fired from a mobile launcher. During the flight its scanning work is done from a stable altitude, the payload and the spent motor are returned to the ground gently by parachute enabling the recovery of the data. One most important limitations of this system is to ensure that the descending rocket not going to cause damage.
6.2.3 Space-borne Observation Platforms
In spaceborne remote sensing, sensors are mounted on-board a spacecraft (space shuttle or satellite) orbiting the earth. Space-borne or satellite platform are onetime cost effected but relatively lower cost per unit area of coverage, can acquire imagery of entire earth without taking permission. Space borne imaging ranges from altitude 250 km to 36000 km.
Spaceborne remote sensing provides the following advantages:
Large area coverage;
Frequent and repetitive coverage of an area of interest;
Quantitative measurement of ground features using radiometrically calibrated sensors;
Semi-automated computerised processing and analysis;
Relatively lower cost per unit area of coverage.
There are two types of well recognized satellite platforms- manned satellite platform and unmanned satellite platform.
Manned Satellite Platforms: Manned satellite platforms are used as the last step, for rigorous testing of the remote sensors on board so that they can be finally incorporated in the unmanned satellites. This multi- level remote sensing concept is already presented. Crew in the manned satellites operates the sensors as per the program schedule. Information on a series of NASA’s manned satellite programs are given in table 6.1.
Table 6.1: Manned satellite programs of NASA
International Space Station
Nov 02, 2000
Mar 10, 2001
Aug 12, 2001
June 07, 2002
Nov 25, 2002
Feb 01, 2003
Apr 18, 2003
Oct 20, 2003
Apr 17, 2004
Three to Seven
1st Station Crew Arrived
2nd Station Crew Arrived
3rd Station Crew Arrived
4th Station Crew Arrived
5th Station Crew Arrived
6th Station Crew Arrived
Space Shuttle Columbia
7th Station Crew Arrived
8th Station Crew Arrived
9th Station Crew Arrived
Head- held Camera
Head-head Camera, LFC, Sir , MOMS
Multiple sensors for remote sensing and a range of laboratory equipments for conducting physics-chemical and biological experiments. It is planned to serve as the base for launching smaller unmanned satellites into polar orbits from which remote sensing data can be relayed to earth stations. Crew from the Space station can also go to these polar satellites to repair and refuel them. Space Shuttle to provide transportation of Astronauts and necessary cargo between earth and the Space station.
(Source: Panda, 2005)
Unmanned Satellite Platforms
Landsat series, SPOT series and IRS series of remote sensing satellite, NOAA series of meteorological satellites, the entire constellation of the GPS satellites and the GOES and INSAT series of geostationary environmental, communication, television broadcast, weather and earth observation satellites etc are examples of unmanned satellite category.
Keywords: Platform, Air borne, Space-borne, Manned Satellite, Unmanned Satellite
Panda. B. C., 2005, Remote sensing principles and applications, Viva Books Pvt. Ltd., pp. 73-78.
Bhatta, B.2010, Remote Sensing and GIS, Oxford University Press, New Delhi, pp. 40-42.
www.crisp.nus.edu.sg/~research/tutorial/spacebrn.htm; Sep17, 2012.
www.e-education.psu.edu/lidar/l2_p4.html; Sep17, 2012.