The Objective of Soil Resource Mapping (SRM) is to demarcate and identify priority watershed in the catchmnert area on 1:50,000 scale.It provides information on physiography,slope, soil depth, surface texture, land use ,land cover, surface condition and existing management practices

Methodology for Soil Resource Mapping:-

The steps involved for conducting the soil resource mapping using remote sensing technique and generation of digital database are as follows.

·            Development of Legend

·             Preparation of Base Map 

·            Delineation of Landscape/ Geological boundary

·             Delineation of Physiographic Units

·             Delineation of Slope Boundary

·             Delineation of Land use boundary

·             Pre-field Interpretation

·             Selection of Sample Strips

·             Ground Truthing and Field Work

·              Final Interpretation, Validation and Finalisation of Maps

Development of Legend: The genesis and formation of soils depend on various factors like geology/ parent material, physiography, slope, land use/ land cover, climate etc. Keeping this in view, five level of delineation has been adopted to formulate the legend for soil resource mapping using visual interpretation technique as follows: 

Level-1: Landscape/ Geology (i.e. BA for Basaltic Landscape)  
Level-2: Physiography (i.e. z for Pediplains) 
Level-3: Slope (i.e. 3 for Very gently to gently slope) 
Level-4: Land Use/ Land Cover (i.e. a for cultivated under rainfed condition)  
Level-5: Soil series association and erosion (i.e. 1, 2, 3 ……..)
Thus the complete mapping symbol would be BAz3a1

Table 1: Landscape / Geology:-

Table 2: Physiographic Units:-

Table 3: Slope Classes:-

Table 4: Land Use/ Land Cover:-

Table 5: Soil Association:-

Preparation of Base Map: Base map is prepared from Survey of India (SOI) Topographic sheets on 1:50K scale on 75 micron tracing film. Four corner points (Tic Points) of the topographic sheet with their geographic coordinate, administrative boundaries (State/ District/ Tehsil) major settlements, drainage lines, canals, railways and roads drawn on the base maps.

Delineation of Landscape/ Geological Boundary: Landscape/ geological boundaries are delineated on the base map with help of, SOI topographic sheet, geological map and geo-morphological map.

Preparation of Slope-cum-Physiography Map: Slope map is prepared from Survey of India topographic sheet on 1:50K scale by drawing lines following contour lines on the base map and defining area between them into various slope classes (range of slope) which are, in turn, translated into various physiographic units based on its location on the ground.

Delineation of Land Use Boundary: All notified forest and other land use boundaries available on toposheet are drawn.

Pre-field Interpretation: Soil information is derived indirectly from imagery by studying reflectance pattern of surface feature portrayed on the image. Image elements, e.g. tone, texture, colour, size, shape, pattern, location and association, are used to extract the desired information. These discernable variations are correlated with geology, physiography, land use/ land cover condition and slope classes and possible mapping units/ association of soil classes are interpreted. Further, detailed and careful study of subtle differences within discernible classes is carried out to segregate individual soil class (homogenous in itself within permissible limits of soil characteristics).

An interpretation key is developed to segregate discernible image units and defined in terms of image elements. A combination of characteristics e.g. tone / colour, texture, size, shape, pattern, shadow, location, association that enable to identify an object on an image is called interpretation key. Thus, a valid correlation between image characters and soil and landscape characters is established and the interpretation is carried out accordingly.

Major drainage lines and/ other permanent features of the base map are matched with the same features visible on the imagery. A soil boundary is delineated within each mapping unit (showing composite unit of landscape/geology, physiography, slope, land use/land cover) by studding image elements and a mapping unit is assigned by considering the image interpretation key. The image interpretation key and mapping legend is modified wherever applicable.

Selection of Sample Strips: Sample areas are selected for ground truth verification to establish correlation between spectral signature of the image and soil and its associated land features. Sample areas are selected by drawing well distributed sample strips so as to represent all landscapes/geology, physiography, slopes and soils. Sample strips are selected along a catena to cover all types of variation in the soils.

Ground Truth and Field Work: Selection of areas for detailed field investigation are made keeping the number of tentatively defined soil classes, traficability of the area and total area under study. Thus, all the tentatively identified soil classes are studied in field for determination of soil and land characteristics, morphological characteristics and relate them with image characteristics.

A rapid traversing of the area is undertaken to study the broad landscape and soil and also to locate sample strip. Profiles are studied at different slope range along a catena to examine all types of soils available in a catena. Thus at least three profiles are examined to establish a tentative soil series. Soil samples are collected to carryout physical, chemical and physico-chemical analysis.

For each mapping unit, a number of observations are collected through profile examination and auger bore/ mini pit and correlated with its image signature. Well distributed observations are taken to cover all quadrants of a toposheet. Around 15-20% of the total area is studied on the ground covering all the tentatively identified soil mapping units.

Finally, each mapping unit is to be described by a set of soil and land characteristics, like depth, colour, texture, association of soil series, erosion, land use, physiography etc. along with its image characteristics. This information is for final interpretation of satellite data.

Final interpretation, Validation and Finalisation of Maps: Soil series are classified and wherever needed, association of soil series is checked and corrected. Mapping legend is to be finalized according to ground truth data by merging mapping units/ developing new mapping unit and maps are corrected accordingly. To ensure correct identification of soil classes and their accurate mapping, validation of the SRM is carried out by undertaking random ground checks. Based on validation findings, improvement in the mapping is made wherever needed.

Preparation of Line Maps: All four tic points of the toposheet are drawn on a new tracing film along with their geographic coordinates. All soil boundaries of the final map are transferred using 0.2 mm tracing pen. State, district and tehsil/ block boundaries are transferred from SOI toposheet on the tracing film.

Data Processing and Report Generation: If digital map is generated, area is automatically calculated after building the topology. Otherwise, area is calculated using a plnimeter. These data are processed to develop different tables and figures for report generation.

 Development of Digital Spatial Database

Preparation and Scanning of Line Map: Toposheet-wise line maps are prepared onto 75 micron tracing film by drawing four corner points of toposheets along with geographic coordinates and only soil boundaries are transferred from soil map using 0.2 mm black ink pen. These line maps are scanned and saved as black and white binary *.tif format.

Raster to Vector Conversion: The raster *.tif files are converted into vector using different commands/ modules. 

Editing of Arcs/ Lines: After converting Grid file to Vector file i.e. Coverage, editing of arc features is done. Unwanted line features are removed using different commands like select, split, delete etc. and to close polygon boundaries, add, extend, etc. commands are used.

Labeling of Soil Mapping Units: After arc editing, labeling is done to assign a unique numerical value to all polygons belong to a particular soil Mapping unit. A unique numerical value as user-id is added to all labels falling within all polygons belong to a particular Soil Mapping unit

Georeferencing: Conversion of digitizer coordinate system to geographic coordinate system is known as Georeferencing.

Edge Matching: Edge matching is the process of verification of contiguity of boundaries having same soil mapping unit. Edge matching with its neighbor toposheets is done one after another. Edge Matching involves adding, deleting and reshaping of arcs.

Mosaicing of Coverages: Mosaicing of all coverages done using ‘APPEND’ command. Editing of arc is done to close the soil boundaries between two toposheets where as editing of point is done to remove additional labels having same user-id with in one polygon.

Extraction of District Area: As per NRIS documents, only one district boundary coverage is to be used to generate all thematic layers. Therefore, the district boundary coverages supplied by NRSA/DOS in Geographic Coordinate System is used to extract soil layer from the appended coverage. ‘CLIP’ command is used for this purpose. After clipping, editing of arcs and labels is done again to close all polygon and to remove unwanted labels or to add labels in unlabelled polygons

Transformation of Projection: Coverage having geographic coordinate is transformed into Polyconic Projection with Everest Datum.

Development of Non-spatial Datasets:-

Non-spatial Datasets are created as per the Design and Standards of NRIS using ‘Soil Resource Data Model’ developed on M S Access platform.

Development of Series Code: A 16 digit character code (AA-BB-CC-DD-EE-FF-GG-HH) is assigned to each soil series as follows:  

·                     Order                                   AA   (2 Characters),  

·                     Sub-order                            BB   (2 Characters),  

·                     Great Group                        CC   (2 Characters) ,  

·                     Sub-group                            DD (2 Characters),  

·                     Texture-Family                    EE (2 Characters),  

·                     Mineralogy-Family              FF (2 Characters),  

·                     Temperature-Family            GG (2 Characters),  

·                     Series                                   HH (2 Characters)

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