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# Unit 1 introduction to remote sensing

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21 Sep 2020
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### Unit 1 introduction to remote sensing

1. UNIT- I INTRODUCTION TO REMOTE SENSING
2. INTRODUCTION • Remote sensing is the science and art of obtaining information about an object, area, or phenomenon through the analysis of data acquired by a device that is not contact with the object, area, or phenomenon under investigation. • The remotely collected data can be of many forms, including variations in force distributions, acoustic wave distributions, or electromagnetic energy distributions.
3. ELECTROMAGNETIC RADIATON &SPECTRUM • EMR is a dynamic form of energy that propagates as wave motion at a velocity of c = 3 x 10*10 cm/sec. The parameters that characterize a wave motion are wavelength (λ), frequency (ν) and velocity (c) (Fig. 2). The relationship between above is c = νλ • Visible light is only one of many forms of electromagnetic energy. Radio waves, ultraviolet rays, radiant heat, and X-rays are other familiar forms. All this energy is inherently similar and propagates in accordance with basic wave theory. • In remote sensing, it is most common to categorize electromagnetic waves by their wavelength location within the electromagnetic spectrum. The most prevalent unit used to measure wavelength along the spectrum is the micrometer ð Þ m . A micrometer equals 13106m.
4. ELECTROMAGNETIC SPECTRUM
5. . • Before radiation used for remote sensing reaches the Earth's surface it has to travel through some distance of the Earth's atmosphere. Particles and gases in the atmosphere can affect the incoming light and radiation. These effects are caused by the mechanisms of scattering and absorption. • Scattering occurs when particles or large gas molecules present in the atmosphere interact with and cause the electromagnetic radiation to be redirected from its original path. How much scattering takes place depends on several factors including the wavelength of the radiation, the abundance of particles or gases, and the distance the radiation travels through the atmosphere. There are three (3) types of scattering which take place. • Rayleigh scattering • Mie scattering • Nonselective scattering • Rayleigh scattering occurs when particles are very small compared to the wavelength of the radiation • Mie scattering occurs when the particles are just about the same size as the wavelength of the radiation • nonselective scattering occurs when the particles are much larger than the wavelength of the radiation INTERACTION WITH EARTH SURFACE
6. CHARACTERISTICS OF REMOTE SENSING Characteristics of Remote Sensing Remote sensing is characterised by; Sensor Stage (satellite, plane, kite, ground based) View (angle of view) Type of radiation sensed(visible light, infrared, radar) Time of capture
7. TYPES OF SENSORS • Remote sensing instruments are of two primary types— • ACTIVE SENSORS, provide their own source of energy to illuminate the objects they observe. An active sensor emits radiation in the direction of the target to be investigated. The sensor then detects and measures the radiation that is reflected or backscattered from the target. • PASSIVE SENSORS, on the other hand, detect natural energy (radiation) that is emitted or reflected by the object or scene being observed. Reflected sunlight is the most common source of radiation measured by passive sensors
8. REMOTE SENSING PLATFORMS Remote sensing platforms can be classified as follows, based on the elevation from the Earth’s surface at which these platforms are placed. Ground level remote sensing o Ground level remote sensors are very close to the ground o They are basically used to develop and calibrate sensors for different features on the Earth’s surface. Aerial remote sensing o Low altitude aerial remote sensing o High altitude aerial remote sensing Space borne remote sensing o Space shuttles o Polar orbiting satellites o Geo-stationary satellite
9. AIRBORNE AND SPACEBORNE REMOTING SENSING • In airborne remote sensing, downward or sideward looking sensors mounted on aircrafts are used to obtain images of the earth's surface. Very high spatial resolution images (20 cm or less) can be obtained through this. However, it is not suitable to map a large area. Less coverage area and high cost per unit area of ground coverage are the major disadvantages of airborne remote sensing. While airborne remote sensing missions are mainly one-time operations, space-borne missions offer continuous monitoring of the earth features. • LiDAR, analog aerial photography, videography, thermal imagery and digital photography are commonly used in airborne remote sensing. • In space-borne remote sensing, sensors mounted on space shuttles or satellites orbiting the Earth are used. There are several remote sensing satellites (Geostationary and Polar orbiting) providing imagery for research and operational applications. While Geostationary or Geosynchronous Satellites are used for communication and meteorological purposes, polar orbiting or sun- synchronous satellites are essentially used for remote sensing. • The main advantages of space-borne remote sensing are large area coverage, less cost per unit area of coverage, continuous or frequent coverage of an area of interest, automatic/ semiautomatic computerized processing and analysis. However, when compared to aerial photography, satellite imagery has a lower resolution. Landsat satellites, Indian remote sensing (IRS) satellites, IKONOS, SPOT satellites, AQUA and TERRA of NASA and INSAT satellite series are a few examples.
10. IMAGE DATA CHARACTERSTICS • The most significant characteristic of the image data in a remote sensing system is the wavelength, or range of wavelengths, used in the image acquisition process. If reflected solar radiation is measured images can, in principle, be recorded in the ultraviolet, visible and near- to-middle infrared range of wavelengths. DIGITAL IMAGE DATA FORMATS • In order to properly process remotely sensed data, the analyst must know how the data is organized and stored on digital tapes and how the data are processed by computers and software • There are four major data formats used by government and commercial data suppliers: • 1 Band Interleaved by Pixel (BIP) Format • 2 Band Interleaved by Line (BIL) Format • 3 Band Sequential (BSQ) Format
11. . BAND INTERLEAVED BY PIXEL FORMAT (BIP) One of the earliest digital formats used for satellite data is band interleaved by pixel (BIP) format. This format treats pixels as the separate storage unit. Brightness values for each pixel are stored one after another. It is practical to use if all bands in an image are to be used. BAND INTERLEAVED BY LINE FORMAT (BIL) Just as the BIP format treats each pixel of data as the separate unit, the band interleaved by line (BIL) format is stored by lines. Below Fig shows the logic of how the data is recorded to the computer tape in sequential values for a four band image in BIL format. Each line is represented in all four bands before the next line is recorded. Like the BIP format, it is a useful to use if all bands of the imagery are to be used in the analysis. If some bands are not of interest, the format is inefficient if the data are on tape, since it is necessary to read serially past unwanted data BAND SEQUENTIAL(BSQ) FORMAT The band sequential format requires that all data for a single band covering the entire scene be written as one file (see Fig. 2-3.3). Thus, if an analyst wanted to extract the area in the center of a scene in four bands, it would be necessary to read into this location in four separate files to extract the desired information. Many researchers like this format because it is not necessary to read serially past unwanted information if certain bands are of no value, especially when the data are on a number of different tapes. Random-access optical disk technology, however, makes this serial argument obsolete
12. . BAND INTERLEAVED BY PIXEL FORMTA . . . BAND SEQUENTIAL FORMAT .
13. CARTOSAT The name cartosat is a combination of cartography and satellite. The cartosat satellites are a series of Indian optical earth observation satellites. The are used for earths resource management defence service and monitoring. • Orbit : circular sun synchronous • Nominal Wait Time to Acquire Adjacent Path :11 days • Orbital Repetivity Cycle : 126 days • Local Time of Equator crossing : 10.30 a.m. • Number of Orbits per day : 15 • Orbit period : 97 min • Orbit inclination : 98.87° • Orbit height : ~618 km RADAR IMAGING SATELLITE is a series of radar imaging reconnaissance satellites built by ISRO. They provide all weather earth observation satellites from ISRO. • Regime : Sun-synchronous • Apogee altitude : 536.38 km • Inclination : 97.554 degrees • Period : 95.49 minutes • Mean motion : 14 • The revisit period is 25 days with an advantage of a12 day inner cycle in the CRS (Coarse Resolution ScanSAR) mode RISAT
14. MODIS • The Moderate Resolution Imaging Spectroradiometer (MODIS) is a playload imaging sensor built by Santa Barbara Remote Sensing that was launched into earth orbit by NASA in 1999. With its low spatial resolution but high temporal resolution, MODIS data are useful to track changes in the landscape over time. Examples of such applications are the monitoring of vegetation health by means of time- series analyses with vegetation indices, long term land cover changes (e.g. to monitor deforestation rates), global snow cover trends,] water inundation from pluvial, riverine, or sea level rise flooding in coastal areas,[ change of water levels of major lakes such as the Aral see, and the detection and mapping of wildland fires. • Orbit : 705 km, 10:30 a.m. descending node (Terra) or 1:30 p.m. ascending node (Aqua), sun-synchronous, near-polar, circular. • Inclination : 98.2° • Repetitive cycle : 16 days. ADVANCED SPACEBORNE THERMAL EMISSION AND REFLECTION RADIOMETER is a global digital evaluation model V002 with 30 m reduction was used to extract information on terrain surface and drainage network at the micro-catchment. ASTER satellite image data contribute to a wide array of global change related application areas including the dynamics of vegetation and ecosystems monitoring of harzards, geology and soils land surface climatography, hydrology glacier changes, land cover change and the generation of digital elevation models(DEMs). • Altitude : 705km • Orbit : polar sun synchronous • Repetitive cycle : 16 days • Inclination : 98.3° • Equator crossing time : 10:30AM (north to south) ASTER
15. . IRS INDIAN REMOTE SENSING SATELLITE is designed to extract information on natural resources IRS has a wide range of applications such as agricultural and inventory of forest resources, geological mapping, water resource Orit : sun synchronous Altitude : 904km Inclination : 99.03° Repetitive cycle : 22 days LANDSAT Land remote sensing satellite is the first generation satellite which can record the visible and near visible wavelengths around the ground. Altitude of 570 miles to gather information on earth resource in a systematic and repetitive manner RBV, MSS, TM sensors are used. Inclination : 99.09° Repetitive cycle : 18,16 days. Applied in agriculture forestry civil engineering and land resources. SPOT Satellite Pour l’Observation de la Terre also caleed as satellite for earth observation with high resolution. High resolution images are being captured by spot which are used for many application like urban planning and growth assessment, planning and growth assessment planning for transportation and extration for natural resources. Orbit : Sun-Synchronous Altitude : 832 km Inclination : 98.7° Equatorial crossing time : 10:30 hrs Repetitive cucle : one for every 26 days.
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