Remote sensing

1. Dhwani Shah Assistant Professor Bhaikaka Centre for Human Settlements APIED, V.V. Nagar dhwani.shah@apied.edu.in

2.   What is Remote Sensing?  Need for Remote Sensing  Who uses Remote Sensing and why?  Remote Sensing Process  Principle behind Remote Sensing  Sensors and Platforms  Resolutions  Spatial  Spectral  Temporal  Radiometric Contents

3.  Remote sensing is the science of acquiring information about the Earth's surface without actually being in contact with it. This is done by sensing and recording reflected or emitted energy and processing, analyzing, and applying that information. What is Remote Sensing?

4.   Systematic data collection  Repeatability  Global Coverage  Inaccessible area- sometimes only solution  Multipurpose information Need for Remote Sensing

5.   the geographer, who looks for changes on the Earth's surface that need to be mapped;  the forester, who needs information about what type of trees are growing and if they have been affected by disease or fire;  the environmentalist, who wants to detect, identify and follow the movement of pollutants such as oil slicks on the ocean;  the geologist, who is interested in finding valuable minerals; Who uses Remote Sensing and why?

6.  the farmer, who wants to keep an eye on how his crops are growing and if they've been affected by drought, floods, disease or pests;  the ship captain, who needs to find the best route through the northern ice packs;  the firefighter, who sends out his crews based on information about the size and movement of a forest fire.  the Urban Planner, who wants to map and monitor land cover, land use, morphology ( the study of the form of human settlements and the process of their formation and transformation) etc.

7.  Remote Sensing (RS) Process Energy Source Atmosphere Target Sensor Transmission Interpretation Application Standby- relaying/ passing on information when satellite not in site

8. 1. Energy Source or Illumination (A) – the first requirement for remote sensing is to have an energy source which illuminates or provides electromagnetic energy to the target of interest. 2. Radiation and the Atmosphere (B) – as the energy travels from its source to the target, it will come in contact with and interact with the atmosphere it passes through. This interaction may take place a second time as the energy travels from the target to the sensor. 3. Interaction with the Target (C) - once the energy makes its way to the target through the atmosphere, it interacts with the target depending on the properties of both the target and the radiation.

9. 4. Recording of Energy by the Sensor (D) - after the energy has been scattered by, or emitted from the target, we require a sensor to collect and record the electromagnetic radiation. 5. Transmission, Reception, and Processing (E) - the energy recorded by the sensor has to be transmitted, often in electronic form, to a receiving and processing station where the data are processed into an image (hardcopy and/or digital). 6. Interpretation and Analysis (F) - the processed image is interpreted, visually and/or digitally or electronically, to extract information about the target which was illuminated. 7. Application (G) - the final element of the remote sensing process is achieved when we apply the information we have been able to extract from the imagery about the target in order to better understand it, reveal some new information, or assist in solving a particular problem.

10. Electromagnetic energy reaching the earth's surface from the Sun is reflected, transmitted or absorbed. Specific targets have an individual and characteristic manner of interacting with incident radiation that is described by the spectral response of that target. Egs-soils of differed types, water with varying degrees of impurities, or vegetation of various species Principle behind RS

11.  Electromagnetic Radiation (EMR) like radio waves, infrared (heat) waves make characteristic patterns as they travel through space. Each wave has a certain shape and length. The distance between peaks (high points) is called wavelength.  The light which our eyes - our "remote sensors" - can detect is part of the visible spectrum. The visible wavelengths cover a range from approximately 0.4 to 0.7 μm (micrometre; 1 μm= 1×10−6 of a metre).

12. The electromagnetic spectrum ranges from the shorter wavelengths (including gamma and x- rays) to the longer wavelengths (including microwaves and broadcast radio waves). There are several regions of the electromagnetic spectrum which are useful for remote sensing. Electromagnetic Spectrum

13.  An image is a two-dimensional representation of objects in a real scene. Remote sensing images are representations of parts of the earth surface as seen from space.  A digital image comprises of a two dimensional array of individual picture elements called pixels arranged in columns and rows.  Each pixel represents an area on the Earth's surface. A pixel has an intensity value and a location address in the two dimensional image. Data Recording

14.  Sensor A device that records Electromagnetic Energy Platform Carrier bed used to carry a sensor Platforms and Sensors

15.  Platforms  Platforms are used to house the sensors which obtain data for remote sensing purposes.  The distance between the target being imaged and the platform, plays a large role in determining the detail of information obtained and the total area imaged by the sensor.  Platforms are-  Ground based  Airborne eg. Aircraft, Drone  Space borne eg. Satellite

16.  Passive sensors- Passive system record energy reflected or emitted by a target illuminated by sun. e.g. normal photography, most optical satellite sensors  Active sensors- Active system illuminates target with energy and measure reflection. e.g. Radar sensors, Laser altimeters RADAR(Radio Detection and Ranging), LIDAR(Light Detection and Ranging) Types of Sensors

17.  The path followed by the satellite is called its orbit.  Types of Satellite Orbits  Polar  Equatorial  Inclined  Satellite orbits are designed according to the capacity and objective of the sensors they carry. Depending on their altitude, orientation and rotation relative to the earth, satellites can be categorized as-  Geostationary  Polar orbiting and Sun-synchronous Satellite Orbits

18.   Satellites at very high altitudes (approximately 36,000 kilometres), view the same portion of the Earth's surface at all times have geostationary orbits.  Geostationary satellites are always located directly above the equator with a zero angle of inclination.  These satellites, revolve at speeds which match the rotation of the Earth so they seem stationary, relative to the Earth's surface.  This allows the satellites to observe and collect information continuously over specific areas. Weather and communications satellites commonly have these types of orbits. Geo-Stationary Satellites

19.  The remote sensing platforms are designed to follow an orbit (basically north-south) which, in conjunction with the Earth's rotation (west-east), allows them to cover most of the Earth's surface over a certain period of time.  These satellites cover each area of the world at a constant local time of day. At any given latitude, the position of the sun in the sky as the satellite passes overhead will be the same within the same season. This ensures consistent illumination conditions when acquiring images in a specific season over successive years, or over a particular area over a series of days. This is an important factor for monitoring changes between images or for mosaicking adjacent images together. Sun-Synchronous Satellite

20.  As a satellite revolves around the Earth, the sensor "sees" a certain portion of the Earth's surface. The area imaged on the surface, is referred to as the swath. Swath

21.  Ability of the system to render the information at the smallest discretely separable quantity  in terms of distance (Spatial),  wavelength band of EMR(Spectral),  Time (Temporal) and  Radiation (Energy) RESOLUTIONS

22.   Spatial resolution refers to the amount of detail that can be detected by a sensor/ Smallest unit-area measured.  Images where only large features are visible are said to have coarse or low resolution. In fine or high resolution images, small objects can be detected.  Detailed mapping of land use practices requires a much greater spatial resolution SPATIAL RESOLUTION

23.  Spatial resolution of passive sensors depends primarily on their Instantaneous Field of View (IFOV).  The IFOV is the angular cone of visibility of the sensor (A) and determines the area on the Earth's surface which is "seen" from a given altitude at one particular moment in time (B). The size of the area viewed is determined by multiplying the IFOV by the distance from the ground to the sensor (C). This area on the ground is called the resolution cell and determines a sensor's maximum spatial resolution.

24. Fine/ high resolution Coarse/ low resolution Source: http://www.crisp.nus.edu.sg/

25.  Spectral Resolution describes the ability of a sensor to define fine wavelength intervals  This refers to the number of bands in the spectrum in which the instrument can take measurements  Higher Spectral resolution = better ability to exploit differences in spectral signatures SPECTRAL RESOLUTION

26.  Panchromatic- A single band image generally displayed as shades of gray.  Multispectral- A multispectral image consists of a few image layers, each layer represents an image acquired at a particular wavelength band.  Hyperspectral- A hyperspectral image consists of about a hundred or more contiguous spectral bands. The precise spectral information contained in a hyperspectral image enables better characterisation and identification of targets. Hyperspectral images have potential applications in such fields as precision agriculture (e.g. monitoring the types, health, moisture status and maturity of crops), coastal management.

27.  Spectral resolution describes the ability of a sensor to define fine wavelength intervals. The finer the spectral resolution, the narrower the wavelength range for a particular channel or band.

28. Source: IIRS, ISRO Presentation

29. False Colour Composite

30.  Revisit time (temporal resolution) = time between two successive image acquisitions over the same area  Represents the frequency with which a satellite can re-visit an area of interest and acquire a new image.  Depends on the instrument’s field of vision, and the satellite’s orbit. TEMPORAL RESOLUTION

31.  The time factor in imaging is important when:  Short-lived phenomena (floods, oil slicks, etc.) need to be imaged  Multi-temporal comparisons are required (e.g. the spread of a forest disease from one year to the next, Sprawl of the city over the years)  The changing appearance of a feature over time can be used to distinguish it from near similar features (wheat / maize)

32.   The radiometric characteristics of an image describe the actual information content in an image. Its ability to discriminate very slight differences in energy.  Sensitivity to the magnitude of the electromagnetic energy determines the radiometric resolution. RADIOMETRIC RESOLUTION

33. Source: http://www.crisp.nus.edu.sg/

34.   The maximum number of brightness levels available depends on the number of bits used in representing the energy recorded. Thus, if a sensor used 8 bits to record the data, there would be 2^8= 256 digital values available, ranging from 0 to 255.  Image data are generally displayed in a range of grey tones, with black representing a digital number of 0 and white representing the maximum value (for example, 255 in 8-bit data).

35. By comparing a 2-bit image with an 8-bit image, we can see that there is a large difference in the level of detail discernible depending on their radiometric resolutions. Source: IIRS, ISRO Presentation

36. Source: IIRS, ISRO Presentation Digital number in remote sensing systems, a variable assigned to a pixel, usually in the form of a binary integer in the range of 0–255 (i.e. a byte). The range of energies examined in a remote sensing system is broken into 256 bins.

37. Source: IIRS, ISRO Presentation

38.   http://learn.arcgis.com/en/projects/get-started- with-imagery/app/  http://learn.arcgis.com/en/projects/get-started- with-imagery/lessons/view-the-world-with-landsat- imagery.htm Understanding Imagery

39.   Collect information (Spatial, Spectral, Temporal & Radiometric resolution, Swath, which country launched it) about the following satellites in groups of five-  Code no. 1 to 5- IKONOS  Code no. 6 to 10- LANDSAT (1 to 8)  Code no. 11 to 15- SPOT (1 to 7)  Code no. 16 to 20- QuickBird  Code no. 21 to 25- NOAA (National Oceanic and Atmospheric Administration)  Code no. 26 to 30- Cartosat (1, 2, 2A, 2B) Assignment