Architecture M.Arch

Master in Architecture

(GIS)

Architecture M.Arch

Sustainable and Green Building Design

Module Detail

Subject Name M.Arch - Architecture Paper Name GIS

Module Name/Title Satellite Imagery

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Role Name

National Coordinator

Subject Coordinator Dr. Monsingh D. Devadas Paper Coordinator Dr. Pratheep Moses Content Writer/Author (CW) Dr. S. Vijaysagar Content Reviewer (CR) Dr. Pratheep Moses Language Editor (LE)

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INTRODUCTION

Remote sensing is the technique of deriving information about objects on the surface of the earth without physically coming into contact with them. This process involves.

Making observations using sensors (Cameras scanners radiometer radar etc.) mounted on platforms (aircraft and satellites) which are at a considerable height from the earth surface.

Recording the observations on a suitable medium (such as images on photographs films and videotapes or digital data on magnetic tapes). If there is no physical access to the sensor such as in the case of satellite the data is transmitted down to a ground station where it is recorded on magnetic tapes. The ground station therefore needs to have an appropriate tracking antenna and communication link with the satellite.

Corrections to the data to remove geometric and radiometric distortions caused due to motion of the platform relative to earth platform attitude earth curvature non-uniformity of illumination variations in sensor characteristics etc. This can be done either using electro-optical techniques or more popularly by using computers and is called per-processing and generation of output products in the form of photographic enlargements with appropriate rectification. If the pre- processed data is in digital form it is concerted into an image by etching a photographic film using a computer based photo write system. For those who need the data in digital form for analysis and interpretation on computer based systems the final products are provided on magnetic media such as Computer Compatible Tapes (CCTs) cartridge tapes floppy diskettes and digital Audio Tapes (DATs)

1.2 MAKING OBSERVATIONS

1.21. ILLUMINATION USING ELECTROMAGNETIC ENERGY

Just as our eyes need objects to be illuminated by light so that we can see them sensors also need a source of energy to illuminate the earth’s surface. Different forms of electromagnetic energy are utlilsed for this purpose and the most widely used part of the electromagnetic spectrum is the visible region because the atmosphere is transparent in this region. Whenever electromagnetic energy falls on an object, part of it is absorbed, part of it is allowed to pass through and the remaining is either reflected or scattered. The proportion of this distribution is different for different wavelengths of the incident and depends on the nature of the object.

For example Sun light which appears white is actually a mixture of all colours of the spectrum. For practical purpose we can think of it as a mixture of blue green and red colours. If an object completely absorbs all these it appears block whereas it papers white if it reflects all these colours. If an object absorbs blue if more of red and green are absorbed while blue is reflected. In

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other words how much of what colour is reflected or absorbed will determine the colour of objects.

An object appears transparent if it allows most of the energy to pass through and opaque if the transmission component is small.

Besides the interaction with incident energy objects are also continuously emitting energy called self-emission the wavelength and intensity of self-emission depend on colour and surface temperature. Reflected / scattered radiation characteristics and emission characteristic together provide unique spectral signature for a class of similar objects and are useful for their identification.

When we wish to identify objects based on their colour we use sensors which operate in the visible region of the spectrum. Whereas, if we wish to classify objects based on their emission characteristics and surface temperature we use sensors, which operate in the infra-red, middle infra- red and thermal infra-red regions. Often sensors, which operate in both the visible and infrared regions, are utilized.

Atmospheric Windows

Basic interactions between electromagnetic energy and an earth surface feature

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SENSORS

Sensors are devices used for making observations. They consist of mechanism usually sophisticated lenses with filter coatings to focus the area observed on to a plane in which the detectors are placed. These detectors are sensitive to a particular region in which the sensor is designed to operate and produce outputs which are the either representative of the observed area as in case of camera (where light sensitive films are used) or produce electrical signals proportionate to radiation intensity (in case the detectors used are electronic transducers such as Charge Coupled Devices (CCDs).

Sensors which sense reflection /radiation from the earth illuminated by a natural source such as the Sun are called Passive sensors. Examples of such sensors are cameras (photographic and TV)

`multi-spectral scanners and radiometers. Sensors which illuminate the targets with energy and measure the reflected / Scattered radiation from the target are called active sensors. Examples are active radiometers and radar. Sensors can also be classified on the basis of the spectral region in which they operate such as visible near infra-red middle infra-red thermal infra-red microwave etc.

The important sensor parameters are:

Spatial resolution: It is the size of the smallest object that can be discriminated by the sensor. The greater the sensors resolution the greater the data volume and smaller the area covered. In fact area coverage and resolution are inter-dependant and these factors determine the scale of imagery.

Alternatively spatial resolution can be said to be the length of the side of the area on the ground represented by a picture (more commonly know as pixel) on the image.

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Spectral resolution: It is the width of the spectral band and the number of spectral bands in which the image is taken. Narrow bandwidths in certain regions of the electromagnetic spectrum allow us to discriminate various features more easily. Consequently we need to have more number of spectral bands each having a narrow bandwidth and these bands should together cover the entire spectral range of interest.

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Radiometric Sensitivity:It is the capability to differentiate the spectral reflectance/

emittance from various targets. This depends on the number of quantisation levels within the spectral band. In other words the number of bits of digital data in the spectral band (or the number of grey levels) will decide the sensitivity of the sensor.

Basically it is called Intensity/Grey levels

Six bit - 0 – 63 levels – totaling - 64 Seven bit - 0 – 127 levels – totaling - 128 Eight bit - 0 – 225 levels – totaling – 256

And is otherwise called as DN – Digital numbers

Dynamic range: The minimum to maximum that can be faithfully measured by the sensor.

Modulation Transfer Function (MTF): The frequency response of the detector.

ATMOSPHERIC WINDOWS

While passing through the atmosphere electromagnetic radiation is scattered and absorbed by gases and particulates. Besides the major atmospheric gaseous components like molecular nitrogen and oxygen other constituents like water vapour methane hydrogen helium and nitrogen compounds play an important role in modifying the incident radiation and reflected radiation. This causes a reduction in the image contrast and introduces radiometric errors. Regions of the

electromagnetic spectrum in which the atmosphere is transparent are called atmospheric windows.

The atmosphere is practically transparent in the visible region of the electromagnetic spectrum and therefore many of the satellite based remote sensing sensors are designed to called data in this region Some of the commonly used atmospheric windows are:

MULTI-IMAGING

Multi-imaging is an important principle, which has been effectively harnessed, in remote sensing

Multi-spectral imaging refers to viewing a given area in several narrow bands to obtain better identificati0on and classification of multi-station imaging refer to the observations of the same area from different positions of the platform to yield stereoscopic data for obtaining height information.

Multi-data imaging refer to the observations made over the same area on different dates to monitor objects, which are dynamically changing with time (e.g. crop growth.) This is also referred to as temporal study.

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Multi-polarisationimaging refer to observations made with incident energy with different polarisation as in the case of active remote sensing sensors. The response of certain object to different polarisation of incident energy has been found to be very useful for better discrimination of objects.

Multi-directional imaging refer to observations made by varying the look angles of the incident radiation from active sensors. This has a distinct effect on the returns (back scatter) from the objects.

PLATFORMS

As we go higher larger areas can be observed by a sensor which is useful for measuring features (such as rivers, mountain ranges etc.,) providing with what is known as synoptic view.

Since the dawn of civilization the strategic importance of making observations from places at higher elevation than the surrounding areas has been well known. That is the reason why forts were built on hills and elevated places so that in the event of an aggression the king’s generals could survey the battlefield below them and direct their troops while still being secure from the enemy. However the size of objects appears smaller as we go higher and in fact an object neither may nor be seen at all beyond a certain height.

The size of the object that can be discriminated by a sensor depends on the resolving power of the sensor and height of the platform. Remote sensing platform may be balloons aircraft or satellite. Aircraft and satellite constitute two important types of present day platforms.

Aerial remote sensing started a few decades ago with photographic cameras and the technology is now well established with the development of sensors such as multi-spectral scanner magnetometers and synthetic aperture radar. Aircraft remote sensing offers certain advantages such as flexibility of operation over any desired area at any convenient time and high-resolution data for application, which need data in large scales.

Satellite used for remote sensing are generally of two types viz., geo-stationary and near earth polar orbiting Geo-stationary satellite as the name suggests are stationary with respect to the earth and are at an altitude of about 36,000 km. Due to their large distance from earth high- resolution imaging is difficult. These are extensively used for meteorological are one set of satellite under this category.

Near earth polar orbiting satellite on the other hand are at a much lower altitude generally between a few hundred to few thousand kilometers. Since they are at a much lower altitude sensors with higher resolution can be realised. Most useful orbit in this category for remote sensing is the circular near polar sun synchronous orbit. In sun synchronous orbit points at a given latitude (say in a descending pass) will have the same local mean solar time so that we can get approximately similar levels of illumination. The ground trace of the satellite can be made to repeatedly cover an area at intervals of a fixed number of days by suitably selecting the orbit parameters.

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RECORDING DATA

When sensors like cameras of multi-spectral scanners are mounted on aircraft the images are recorded on films or magnetic tapes. Ancillary data such as geographic co-ordinates flightdirection and drift aircraft altitude sensor settings such as film speed aperture exposure time scan rate etc are also recorded simultaneously. When the aircraft lands the films or tapes are physically transported to the laboratory for further processing.

In the case of satellite there is no such possibility of physical retrieval of media containing data. The sensor continuously provides output data as it electronically scans the area below it. This is done line by line across the track and the forward coverage is obtained due to satellite motion.

This data is transmitted by the satellite and is received at the ground station. Since the satellite is moving with respect to earth and its orbit is different days it is necessary to be able to predict its

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position accurately and communicate with it using an antenna capable of tracking it ( the antenna therefore must be capable of there axis movement) during thoseperiods when the satellite passes over the earth station. If one were to draw a radius of approximately 3,000 km around the earth station the enclosed area would be the ground coverage of a remote sensing satellite within the acquisition range of the earth station equipped with an antenna of 10m diameter.

There is a need for a uniform referencing scheme to enable us to know the exact location of the area covered by the image data. Since the satellite covers different areas on different days an orbit calendar which tells us this information is necessary. The data pertaining to the area scanned by the satellite is identified by assigning numbers to the paths that the satellite is programmed to cover. The framing of the image in a given path into number of scenes is done by assigning rows across the path. A path-row reference map, which is unique for each satellite, provides information regarding coverage of a given area by the satellite.

DATA PRE-PROCESSING

The data acquired by a sensor suffers from a number of errors. These errors occur due to various reasons such as:

Imaging characteristics of the sensor comprising of non-linear width of the detector response and responsivity variations between the individual detectors

Non-uniformity of illumination Atmospheric effects

Scene surface characteristics

Stability and orbit characteristics of the platform Motion of the earth and earth curvature

The first three factors contribute to what are popularly known as radiometric errors and the others contribute to geometric errors. The data acquired from a sensor is processed to correct these errors to the maximum extent possible so that the inherent quality of the original information of the scene is brought out in an optimal manner. Geometric errors if left uncorrected result in positional errors. Geometric errors are treated as being either systematic or random.

Systematic errors are those errors caused by factors which can be modelled / predicted and whose magnitude can be known and can therefore be corrected by applying suitable formulae. An example is the correction due to earth rotation in which each successive scan line has to be displaced to correct for the known relative motion between the satellite and earth to remove the image skew.

Random errors on the other hand, are those errors, which cannot be modeled and estimated.

Radiometric errors are corrected by applying correction factors to normalise the variations in detector responses after extensive sensor calibration. The corrected data is loaded onto computer compatible Tapes (CCTs) which can be directly used for digital analysis of the data. Alternatively the processed digital data is converted into analog form using records (photo write systems) in

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which photographic film is exposed. This film is then chemically processed to generate colors or black and white photographic products. These images are used for visual interpretation.

ANALYSIS AND INTERPRETATION

The photographic imagery are interpreted by trained photo interpreters using the fundamental picture elements, viz., tone, texture, pattern, size and shape in order to detect and identify various objects. Aerial photographs are seen through stereoscopic instruments to obtain three-dimensional images. There are many photogrammetric instruments nowadays for photo- interpretation and for transferring the interpreted details on to base maps.

If the data is available in digital form, it can be analysed on interactive computer systems for extracting statistical data or classified for obtaining thematic information about resources or for enhancing / manipulating the desired features on the images. The scene is interactively analysed using computers by comparing with the actual signature of the object collected through field visits.

The system of classification of objects is quite accurate and depends on the dispersion of training sets over the area of the scene. Besides the above digital data is also utilized for edge detection, height extraction etc.

Computer analysis offers several advantages like quick processing of large volumes of data and special images processing possibilities (geometrical and other types of corrections, scale changing, band ratioing, contrast enhancement, edge enhancement, feature enhancement etc.,).

Besides the standard peripherals the digital systems consists of high-resolution display terminals for interaction with the resource scientist and output devices such as plotters. Sample reference ground data is also collected and used conjunctively in order to obtain a more accurate classification.

ADVANTAGES OF REMOTE SENSING

Large area coverage for regional survey for a variety of themes and for identification / classification of features.

Repetitive coverage allows monitoring of dynamic phenomena like crop growth.

Data acquisition over inaccessible areas.

Data acquisition at multiple heights for obtaining data in different scales and resolution.

Same data can be analysed / interpreted for different purposes and applications.

Amenability of remote sensing data to computer processes.

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SATELLITE DATA ACQUISITION

The NRSA earth station complex for acquisition of satellite data is situated at Shadnagar about 55km away from Hydrabad. There are three antenna terminals for receiving data from the IRS-1A & 1B, IRS-P2, Landsat–5, ERS-1 and NOAA Satellites. Data archival and quick look facility, foresight facility for testing the complete data reception chain and support systems for power and air conditioning are also available.

The Landsat 2/3 terminal originally installed in 1997 for reception of Landsat data in S - L band has been suitably upgraded to receive IRS-1A data in X-S band in 1988 from IRS-1B since August 1991 and IRS-P2 since October 1994. The Landsat 4/5 terminal was installed in 1984 for receiving the data in X – S band this terminal also serves as a backup for IRS-1A/1B/P2 data reception. SPOT data was acquired using this terminal from mid1986 to end 1990. Currently this terminal also acquires ERS-1 data.

A separate S-L band terminal was established in 1987 for reception of meteorological data from the NOAA series of satellite. All the three terminals have appropriate reception and tracking systems like pre-amplifiers Up / Down converters, demodulators, servo control systems and pedestal systems. The foresight system is located about 800 m away from the three terminals and consists of three radiating antennas on high tower for alignment, RF gain measurement and error gradient measurement.

The data archival and quick look facility is used for recording data from different satellites on High Density Digital Tapes (HDTs) and quick look display in real time and ancillary data generation for the data acquired Dedicated systems are available most of the missions.

PRODUCT GENERATION

Dedicated pre-processing systems are available for generating products from IRS LANDSAT NOAA, ERS and SPOT missions. Further these systems have been suitably upgraded wherever necessary to support other missions also. The IRS-Data Processing System (IRS-DPS) is a VAX 11/780 and 11/750 based system with array processor two 28 track HDIRs, Frame Sync and Demodulation Unit (FSDU) tape drives and other peripherals and is used for processing IRS- 1A/1BP2 LISS 1& LISS 11 sensor data.

The SOPT-DPS is a Micro VAX-II based system consisting of three HDTRs Arry Processors Input / output Computers Frame Synchronization and decommutation units display systems digitizer and other peripherals. This system is capable of processing SPOT TM IRS-1A and 1B data.

The TMDPS is a VAX 11/78 and VAX 11/750 based systems with two HDTRs FSDUs array processor display and other peripherals. This system is capable of processing Landsat TM data.

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The MSS-DPS is a PDP-11/55 based system with 2 HDTRs (14-track) FSDU Array processor quick look display and other peripherals. This system is capable of processing Landsat MSS and NOAA data.

The MET – DPS is a Micro VAX-II based system, which can be used for data analysis of all types of satellite data. The system is being used for processing and analysing NOAA data. The Master Flexible System (MFS) is a Micro VAX-1 based system consisting of three HDTRs Input / Output Computer display system and other peripherals. This system is capable of processing IRS TM, SPOT and ERS-1 data.

There are the colour filming systems and three Block & White filming system for generating master films from pre-processed data. Two PC-AT based systems for floppy/Cartridge product generation VAX 3400 based IRS Precision and data Quality Evaluation (DQE) system, Micro VAX based analysis and GIS system B/W and colour scanners and HDDT/CC cleaner/evaluation system are some of the other facilities available to support product generation. An archive containing data acquired during the past decade comprising of more than 6000 HDDTs provides access to old data.

PHOTO PROCESSING

NRSA has a well-equipped photo processing facility to cater to aerial and satellite photoproducts generation besides photography. Colour and B&W prints and transparencies in various scales / magnification can be generated in large volumes. The facility consists of:

Film processors for colour negative colour positive Black & White negative and aerial colour films

Multipurpose Processors

Paper processors (colour and B&W) Printers / Enlargers

General photography facility

PRODUCT DISSEMINATION

The supply of satellite data products is carried out through the NRSA Data Centre (NDC).

AT NDC a computer based integrated information Management System (IIMS) is used fir handing supply of Satellite data to the user community. A computerized catalogue system is also available.

The comprehensive operational package of IIMS caters to the needs of information on accessions, user requests generation of work orders and monitoring status at various stages of product generation.

To ensure dissemination of data of good quality control is adopted during production. Both masters and reproduced products pass through quality Assurance (QA)

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APPLICATIONS

NRSA carries out a number of national level application projects to develop methodologies and to operationalise remote sensing in the country. Besides these NRSA also undertakes user specific projects. About 350 such projects using aerial and satellite data carried out so far.

Some of the areas in which application projects are conducted at NRSA are Water resources

Land Use Geosciences

Agriculture and Soil Forestry

Oceanography Integrated surveys

Facilities for visual interpretation such as optical reflecting projects light tables stereoscopes optical pantograph etc are available along with several PC based digital analysis/ GIS system for digital interpretation Ground truth facilities comprising of several instruments such as spectro- photometer radiometers water quality analyzer di-electric probes etc are available

A cartography facility with an necessary drawing aids and projection instruments along with a map printing facility with high quality multicolour offset printing capability for bringing out good quality maps and publications support the application activities

Remote sensing training courses for working level and decision making level personnel from user organisations are conducted regularly at the NRSA training facility. The duration of these courses range from a few days to several weeks.

TRAINING AT IIRS

NRSA imparts training to the personal from user department at the Indian Institute of Remote Sensing (IIRS) located at DehraDun. IIRS is organized into various divisions to cater to different activities and they are:

Agriculture and Soil

Coastal Processes and Marine Resource Forestry and Ecology

Geology & Geomorphology

Urban & Regional Planning Water Resource

The duration of the training courses range from a few days appraisal courses for decision makers to foundation courses of three months and P.G Diploma courses of ten months. IIRS is well equipped with facilities for interpretation photo processing ground survey and digital analysis (GIS)

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THE MAIN FUNCTION OF NDC

To provide information required for procurement of satellite data products. This includes the description and specification of different types of products. Changes in product specifications from time to time price lists reference maps accession catalogues orbital calendars, order forms etc.,

To provide assistance in the selection of appropriate data and checking the same for data quality and cloud cover using browse facilities.

To process orders and co-ordinate the generation of products at different work centers within the organization.

To check the quality of the products before despatch.

To promote awareness of remote sensing though publications, seminars, exhibitions etc.,

TYPES OF SATELLITE DATA PRODUCTS

Satellite data products can be classified into different types depending upon:

- satellite and sensor - level of pre-processing - media

PRODUCT CLASSIFICATION BASED ON SENSORS

Data from the following sensors were acquired for the periods mentioned against them. Data products can be generated if the data pertaining to the period of interest is available in the archives and is of good quality.

Sensor Satellite Scene Area Period of Acquisition LISS I IRS-1A

IRS-1B

148 x 174 148 x 174

From 1988 & Continuing From 1991 & Continuing LISS II IRS-1A

IRS-1B IRS-P2

74 x 87 74 x 87 67 x 87

From 1988 & Continuing From 1991 & Continuing From Oct 1994 & Continuing

MSS LANDSAT 3

LANDSAT 4 LANDSAT 5

185 x 185 185 x 185 185 x 185

From Aug 1979 to Feb 1983 From 1982 to 1990

From Oct 1994 & Continuing TM LANDSAT 5 170 x 185 From 1984 & Continuing

PLA SPOT ½ 60 x 60 From 1987 to 1990

MLA SPOT ½ 60 x 60 From 1987 to 1990

AVHRR NOAA Series 2925 x 2200 From 1985 & Continuing SAR ERS 1 100 x 100 From 1991 & Continuing

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Depending upon the corrections applied, data products can be classified as

Raw data: Radiometrically and geometrically uncorrected data with ancillary information for processing at user’s end.

Partially corrected products: Geometrically corrected in the across track direction only and radiometrically corrected for detector normalization with ancillary information (stereo products for photogrammetric studies)

Standard Products: Radiometrically and geometrically corrected for systematic errors

Geocoded Products: Systematic corrections with rotation of pixels to align to true north and resampled to standard square pixel. Referenced to a standard Survey of India (SOI) map sheet.

Precision Products: Radiometric and Geometric corrections refined with the use of ground control points to achieve grater locational accuracy.

PRODUCT CLASSIFICATION BASED ON MEDIA

Data products can be broadly classified into two types depending on the output media i.e.

photographic or digital.

Photographic Products

Photographic products can either be in block & white or color. Further they could be either film or paper products. And in films it is possible to have either positive film or negative film. The size of photographic products can vary depending on the enlargement needed and this is specified as 1X, 2X, 4X and so on. The size of film used in film recorders in generally 240 mm and this is the basic master output from which further products are generated.

False Color Composites

When we say color photographic products, it generally means False Color Composites (FCC). FCCs are generated by combining the data contained in 3 different spectral bands into one image by assigning blue, green and red colors to the data in three spectral bands respectively during the exposure of a color negative. The choice of band combinations can be determined depending upon the applicant.

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Preprocessed data in the digital form is converted into photographic form by exposing film to light, which is modulated by the digital data. To prevent loss of information a suitable transformation is applied to the digital data before its conversion and this is called as look Up Table (LUT). Basically there are two types of LUTs viz. Common LUT and Histogram LUT.

Common LUT is a non-linear enhancement applied to the images based on the satellite analysis of different Histograms covering different types of terrains under different illumination conditions. CLUT is commonly used for scene covering large areas. As long as the generalised distribution pattern represent most of the scene distribution pattern colour cast problems are not expected. It ensures that for a given set of digital values in the three bands.

Histo LUT products are individually stretched products where the digital distribution of a scene is stretched to the full dynamic range of the sensor Histo LUT products have better contrast compared to that of products with CLUT

THE DISAVANTAGE OF HISTOLUT

Colour matching of neighbouring scene can not be achieved due to inconsistency in colour rendition in the overlapping areas. Because of extreme stretching especially in the case of flat terrains where in the digital dynamic range is very much narrow the scenes will have too much contrast. In snow bound areas the scene usually become too soft and dark because they cover two extreme radiometric levels. These types of FCC are not useful for temporal studies.

In view of the above it is suggested opt for common LUT whenever large areas covered by many adjacent scenes are to studied. Selection of histogram stretch calls for sufficient information about the terrain brightness range and presence of snow or cloud for establishing the stretch and clipping

TYPES OF PHOTOGRAPHIC PRODUCTS

Different types of photographic products supplied by NDC are :

STANDARD B/W and FCC FILMS:

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Standard products are available in colour and Black & White in the form of 240mm films either as negatives or positives. The scales of the products are listed below:

STANDARD B/W & FCC PAPER PRINTS

Paper prints both B & W and FCC are supplied in various scales. They are 1X (contact prints) 2X (two times enlarged) and 4X (four times enlarged) and 5X (5 times enlarged). Depending upon the enlargement the scale of the product various. The size and scale of these prints are given below.

ANNOTATION ON PHOTOGRAPHIC PRODUCTS

The photographic products contain certain details annotated on the margins. These are useful for identifying scene sensor date of pass processing level band combination etc. A list of details generally annotated on the images is given below and also in the figure.

Product type Data and time of acquisition of data

Sensor used Sub-scene

Band numbers Gain settings

Path and row number Latitude/longitude coordinates Sun elevation and azimuth Resampling method

Map projection Enhancement

Orbit cycle and day Orbit number

Uncorrected centre coordinates Geographic marks

Name of data receiving station Product generation agency Product generation date Satellite identification

DIGITAL PRODUCTS

Processed data is available on a variety of digital media such as CCTs cartridges and floppy diskettes. In future it is planned to supply satellite data on compact disks (CD-ROM) and Digital audio Tapes (DATs). The users need to have appropriate peripherals and software attached to their systems to be able to read the data.

CCT PRODUCTS

NRSA generates distributes digital data on CCTs. In addition to the image data of the required scene the CCT contains the scene identification and location information. Data on CCTs can be supplied in both 1600 bytes per inch (BPL) and 6250 BPL and in band interleaved by line (BIL) and band sequential (BSQ) formats. There are 5 files in the CCT and they are

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Volume Directory File: It is the first file of every logical volume (logical volume is a collection of one or more files recorded continuously and contains one or more bands of a scene) and consists of volume description record which identifies the logical volume and a text record which identifies the data contained in the logical volume.

Leader file: Contains the information such as sensor calibration coefficients processing parameters etc., and the information pertaining to ephemeris such as location and annotation.

Image file: It contains the images data records

Trailor file: It contains the calibration data file

Null Volume Directory files: Shows the end of the logical volume file. The CCT formats for different sensors can be obtained from NDC.

CARTRIDGE DATA PRODUCTS

With the availability of cartridge tape drives data on magnetic tape medium can be provided in an inexpensive and compact manner. Cartridge drives are less expensive than CCT drives and can accommodate large volumes of data.

The following software is required in order to extract the data from the cartridges.

1. Tall grass tape B/W : Tape management system TMS version 2X or higher 2. Disc operating system : IBM PC DOS/MS DOS Ver 2.1 or higher XENIX

These products follow the same format as CCT products.

Floppy Products

These are miniature products, which are useful to users when their study area is small. The cost of data on floppies has been kept very low as a promotional measure and it is convenient for analysing the data on a low cost PC based image analysis system. The data is arranged in three major blocks within the file. These are master, header and image blocks. Each block has one descriptor record and zero or more logical records. The descriptor provides information on the available fields and records. Supplementary data such as orbit, attitude ground control points etc., are not available on a floppy. All files in the master Header section are in ASCII format. Within the image area, the description is in ASCII and image data in binary.

Sensor Segment Size Area (Mints) Area (Sq.Km) Bands (per product

LISS-I 1K x 1K 38.03’ x 38.03’ 74.75 x 74.75 1

LISS-II 1K x 1K 18.32’ x 18.32 37.37 x 37.37 1

TM 1K x 1K 14.56’ x 14.56’ 30.70 x 30.70 1

MLA 1K x 1K 9.54’ x 9.54’ 20.48 x 20.48 1

PLA 1K x 1K 3.95’ x 3.95’ 10.24 x 10.24 1

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Apart from supplying the regular products listed in the price list, NRSA has the capability to supply several types of non-standard products such as:

- Generation of films from CCTs - Generation of photographic outputs

- Transcribing data from one digital media to another - Preparation of mosaics using several scenes

- Scanning services

PRODUCT SELECTION SERVICES

The second stage in product procurement is browsing the data for cloud cover, area coverage, etc. This can be done at the browse facility of NDC, where users can personally screen the data as per their requirement. To facilitate smooth and efficient service to the users, browse section of NDC is equipped with the following browse data and instrument/aids.

BROWSE FACILITIES

Quick look films

These are one band B/W 70-mm film negatives, which are available for IRS LISS & SPOT (PLA, MLA) for all the data acquired between the periods 1988 – 1992 and 1987 – 1990 respectively. These can be used with the help of quick look viewer/enlargers.

Browse Prints

These are B/W paper prints available for all the IRS images acquired over India with a cloud cover less than 60-70%. Each print has a dimension of 10 “x 10” and contains nine 70 mm images corresponding to one LISS I scene in band 3 and eight LISS II sub-scenes four each in band 3 and 4. These are available for the period March 1988 to January 1992.

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These are VHS videocassettes and contain bands 4 data of all the scenes of Landsat 4/5 MSS data acquired between mid 1985 and April 1992. Video cassette players and Televisions are available at NDC to facilitate browsing the data. It is available for TM data from April 1992 to June 1992.

Digital Browse

The process of browsing through film rolls, paper prints or videos can be time consuming and in case of films and paper prints the image size is also very small. To overcome these limitations a digital browsing facility has been installed at NDC. Currently this facility is available for:

1. IRS 1A, 1B, 1C and 1D for data pertaining to January, 1991 onwards 2. Landsat 5 to 8 MT data from June, 1992 onwards and

3. NOAA- AVHRR data from October 1992 onwards

Sub-sampled browse processed imagery of LISS – I band 3 TM Band 4 and AVHRR Band 3 data are directly transferred to a PC based system at NDC. This system consists of an optical disc and a simple image display electronics. Each of the optical discs has a capacity of 640 MB and can store 7,200 LISS – I scenes, 9000 TM scenes and 6500 AVHRR scenes approximately. Once the imagery is transferred to the disc, it can be displayed on a high-resolution 19” B/W monitor. When compared with browse prints, digital browse has a number of advantage such as improved TAT (data can be browsed after 24 hr.) quick retrieval due to automatic operations etc., Shortly browse facility will be provided in color(3 band FCCs).