Remote Sensing and Image Interpretation Speaker Shagufta Akbari Assistant Prof. KL University

contents Introduction Map as a model Spatial elements and terminology Classification of Maps Map Scale Spatial referencing system Computers in map production General software’s in map production Types of data products

Continued …… Image interpretation strategy Levels of interpretation keys Topography Types of Drainage pattern and Texture Erosion Process of image interpretation Basic elements of image interpretation Overview on visual image interpretation equipment

Map as Model Representation of features of earth drawn to scale “A map is a very powerful tool and maps are typical reductions which are smaller than the areas they portray” (Robinson et.al 1984)

Spatial elements and terminology Spatial objects in the real world can be thought of as occurring in four easily identifiable types namely, points, lines, areas and surfaces Points, lines and areas can be represented by using symbols to depict the real world. Surfaces are represented by any combination of these spatial entities. In general, all the geographic surfaces are in two tangible forms, namely, discrete and continuous. Trees, houses, road intersections and similar items are discrete spatial features.

Classification of Maps On the basis of scale Small scale map Large scale map- urban plan map, transportation and network map

Map Scale The ratio between the reduced depiction on the map and the geographical features in the real world is known as the Map Scale Scale expressed in three ways: Fractional scale-the method of representing this type of scale is called representation fraction method

In India commonly used fractional map scales are 1:1,00,000,00; 1:250,000, 1:50,000; 1:25,000 and 1:10,000 Graphical Scale- A line printed on the map and divided into units that are equivalent to some distance The measured ground distance appears directly on the map in graphical representation Verbal Scale- This is an expression in common speech like “an inch to a mile”

Spatial referencing system To locate objects with respect to some reference system Methods of spatial referencing systems Geographic coordinate systems- Denoted by latitude and longitude Rectangular coordinate systems(RCS) Spatial data are in two-dimensional form Relative position- location of any point on the earth’s surface w.r.t RCS Non- coordinate systems Spatial reference with descriptive codes such as postal codes which is numeric in nature

Computers in map production Advantages To make existing maps more at a quicker pace To make existing maps at a cheaper rate To make maps for specific user needs To make map production possible in situations where skilled staff are unavailable To allow experimentation with different graphical representations of the same data

Continued… To facilitate map making and updating when the data are already in digital form To minimize the use of the printed map as a data store and thereby to minimize the effects of classification and generalization on the quality of the data Introduction of automation can lead to a review of the whole map – making process , which can also lead to savings and improvements To create maps in which selection and generalization procedures are explicitly defined and consistently executed

General software’s in map production Arc- GIS ARC- VIEW etc.

Raw data: radiometrically and geometrically uncorrected data Types of data products Depending on correction applied & level of processing RS data products Photographic products such as paper prints, film negatives, diapositives of black and white and FCC False color composite Digital form CCTs computer compatible tapes RS data products Raw data: radiometrically and geometrically uncorrected data Standard data: radiometrically and geometrically corrected data Geocoded products:data: products are north oriented and compatible to survey of India mapsheet Precision product: radiometrically and geometrically corrected data with the use of GCP to achieve greater locational accuracy Geocoded products:data: systematically & geometrically corrected products :data: products are north oriented and compatible to survey of India mapsheet It means overlays of this data with survey of india map can be performed Note: FCC are generated by combininig the data contained in three spectral bands respectively. The choice of band combinations can be determined depending upon application

Image interpretation strategy Visual image interpretation : Process of indentifying what we see on the images and communicate the information obtained from these images to others for evaluating its significance Includes relative locations and extents Use of data products like Satellite single band imageries, FCC for performing image interpretations to extract thematic information for subsequent input to GIS

Levels of interpretation keys Interpretation Keys: Criterion for identification of an object with interpretation elements

Basic elements of image interpretation X, Y location size shape shadow Tone colour Texture Pattern Height & Depth Site, Situation & Association

Size Size of objects in an image is a function of scale Proper photo scale selected depending on the purpose of interpretation Most commonly measured parameters:- length, width, perimeter, area and occasionally volume

Shape Shape of an object is described as the geometric form represented form represented on an image Regular shapes are signs of man-made objects Irregular shapes with no distinct geometrical pattern are signs of a natural environment Regular shapes are signs of man-made objects- buildings, roads and cultivated fields Irregular shapes with no distinct geometrical pattern are signs of a natural environment- water body or a river

Shadow Shadow – usually a visual obstacle for image interpretation Gives height information about towers, tall buildings H object S Shadow

Tone Band of EM spectrum recorded by RS system may be displayed in shades of grey ranging from black to white Tone:- continuous grey scale varying from white to black It refers to relative brightness or colour of objects in an image Note:- Humans differentiate 40- 50 individual shades of grey RS image For eg. In panchromatic photograph Dry sand appears white, while wet sand appears black

Colour more convenient for the identification of object details Texture Characteristics placement & arrangement of repetitions of tone or colour in an image Visual impression of roughness or smoothness of an image region