Photogrammetry Case Study #1: Water Supply Site Suitability Assessment
Our Photogrammetry analysis assessed the suitability of a Water Supply Site located near the town of Chandil in Jharkhand State, India. The ultimate goal of the project was to provide reliable water supply for nearby tribal hamlets suffering from poor water resource management.
Chandil is a census town within the Seraikela Kharsawan district in the state of Jharkhand, India. A census town is one which is not statutorily administered as a town, but nevertheless has a population that has attained urban characteristics. The natural scenery in and around Chandil is unique and picturesque. It is surrounded by green mountains, hills, streams, and rivers. Chandil is located at 22.97°N 86.05°E with an average elevation of 246 metres (807 feet)
|Dam Name||Chandil Dam|
|Type of dam||Earthen / Gravity|
|District Name||Saraikela Kharsawan|
|Lat / Long||22.974663, 86.020807|
|Total Storage Capacity||1,500,000 cubic meters|
|Purpose||Irrigation, Hydroelectric, Drinking / Water Supply|
|Power Generation Capacity||8 MW|
|Construction began||In 1978|
|Project||Hydro-Electric Power Project, Subernarekha Multipurpose Project|
Chandil is rich with the natural resources such as forests. However, local development has been hindered by several causes resulting in scarcity of water scarcity for tribal communities even with the presence of the Chandil dam. SaraniaSat CANEUS personnel assisted TATA Consulting Engineers (TCE) by conducting a photogrammetry project in support of a 85-km-long water supply pipeline installation aimed at mitigating the water scarcity faced by the tribal communities.
As the Chandil region is surrounded by mountains, valleys, and thick forests, TCE was unable to perform a complete, purely ground-based topographic survey as a necessary prerequisite for pipeline installation. Hence, TCE requested the Nest Consulting Service(Bengaluru, India)for Photogrammetry services. SaraniaSat CANEUS personnel were tasked with preparing the site suitability assessment for pipeline installation in the Chandil region. SaraniaSat CANEUS personnel decided to develop a Photogrammetric Solution using Satellite Data.
Satellite Data Used:
CARTOSAT-1 is an Indian satellite – No. 11 in the IRS (Indian Remote Sensing) series and designed to provide quality Earth observation imagery for telemetry and digital mapping applications. CARTOSAT-1 carries two panchromatic sensors capturing forward-looking images (26-degree inclination) and backward-looking images (5-degree inclination). Images are recorded almost simultaneously in both directions along the satellite’s orbital trajectory. The sensors cover a 30-km-wide swath with a resolution of 3m (Forward Looking) and 2.5 m (Backward Looking).
Orthorectification of Cartosat-1 Satellite data
Orthorectification is the process of converting satellite instrument-acquired images into a form suitable for maps by removing sensor, satellite/aircraft motion and terrain-related geometric distortions from raw imagery. Corrections have to take into account the following factors:
- Camera and sensor orientation
- Systematic error associated with the camera or sensor
- Topographic relief displacement
- Earth curvature
By performing block triangulation, the parameters associated with camera and sensor orientation are defined. Using least squares adjustment techniques during block triangulation minimizes the errors associated with camera or sensor instability.
Orthorectification Workflow Schematic
Ground Control Points (GCPs): Block Triangulation in Photogrammetry the process of determining and calculating the 3-dimensional object coordinates by using imagery of the same area acquired from different viewpoints. As a starting point, we need to identify some points with well-known position coordinates (measured using precise Differential GPS survey methods on the ground) that are visible in at least some of the photographs.
These points we call ground control points, or control points, and play an important role in the Block Triangulation process.
Block Triangulation: Once precise locations are assigned to specific pixels in the remote-sensing imagery, a stereo model of the area of interest can be constructed. Next, Block Triangulation is conducted on the stereo model wherein the position and inclination of the camera is calculated for each image acquisition. Also calculated are the X, Y and Z coordinates of “tie points” or pixels belonging to common features between images.
DEM Editing and Contour generation:
A digital elevation model (DEM) can sometimes contain pixels with null or incorrect values. SaraniaSat CANEUS has extensive experience in editing the DEM to smooth out such irregularities to generate a more accurate model which, in turn, can produce more accurate orthorectified images. For example, the processing of nominally flat areas, such as lakes, often contain pixels with erroneous elevation values. Applying a constant elevation value to pixels within these areas significantly improves the DEM and results in a more accurate representation of the lake within the ortho image.
In many cases, a DEM may need conversion from a digital surface model (DSM) to a digital terrain model (DTM). A DSM represents the elevation surface that includes objects, such as buildings and trees, whereas a DTM represents a bare-Earth elevation surface minus these objects. Using a DTM to perform the orthorectification therefore generally results in a more accurate representation. Thus, a DEM that’s initially extracted from overlapping images is most often a DSM. The DSM should be subsequently converted to a DTM, and then edited prior to its use for orthorectification.
SaraniaSat CANEUS’ DEM Editing Service includes:
- Interpolation of height at any terrain point.
- Plots of contours with user-specified contour intervals.
- Volume Calculations which include manmade cuts and fills in the terrain such as in surface mining operations
SaraniaSat CANEUS has proven experience in offering Orthophoto Production services. SaraniaSat CANEUS personnel have successfully delivered on Geospatial projects that require Stereo Pair Imagery Processing, Drone Imagery Processing, Thermal Imagery Processing, RGB & Color-Infrared (CIR) Orthophotography and Black & White Orthophotography. Orthophoto processing involves precise calculations of Planimetric distances with real-life representations of the ground locations being measured.
Orthorectification allows the incorporation of terrain features and objects such as roads, plan views of buildings, railway lines, woodland, rivers and lakes etc. which are accurately positioned within two-dimensional maps. Orthorectification allows subsequent cartographic layering and filtering operations to be conducted c with consistent scale and geometry registration.
SaraniaSat CANEUS’ Orthophoto generation Services include
- Multi-sensor image fusion
- Orthorectification and Orthophoto interpretation
- Color balancing and image Mosaicking
- Object based image classification
- Seamline editing
- Tile cutting