Overview

Aerial Services & Digital Mapping Area (AS&DMA) of National Remote Sensing Centre (NRSC) of ISRO is the only civilian Government entity in the country with end-to-end state-of-the-art infrastructure and capability in the domain of aerial photography, LIDAR and Synthetic Aperture Radar surveys.

Aerial Services & Digital Mapping Area (AS&DMA) has two Beechcraft Super King Air B-200 aircraft in its fleet. The facility has diversified state-of-the-art data acquisition instrumentation like Large Format Digital Camera, Airborne LIDAR, SAR, Analogue metric camera, GPS systems.. AS&DMA also supports special scientific missions. AS&DMA is one stop shop for complete geomatics solutions. It can host a entire gamut of airborne sensors like LFDC, LIDAR, Airborne SAR, multi-spectral scanner system etc. The aircraft can fly from 1000 feet to 30,000 feet above ground level and photo scales from 1:400 up to 1:40,000 can be achieved. The Expertise include Aerial Surveys, Ground Control Surveys, Value-added Services & providing Complete Solutions. The Aerial Survey includes Surveys using Aerial photographic (B&W, Colour, CIR) – Digital Cameras & Airborne Laser Terrain Mapping (LIDAR) / Digital Cameras, Airborne Synthetic Aperture Radar Surveys (SAR). 

Aerial Surveys
--Aerial photographic (B&W, Colour, CIR) – Digital Cameras
--Airborne Laser Terrain Mapping (LIDAR) / Digital Camera
--Airborne Synthetic Aperture Radar Surveys (SAR) 

Ground Control Surveys
--Control surveys with Geodetic GPS receivers, Total stations, EDM and Digital & Auto-Levels Value-added Services
--Generation of Large scale 3D geospatial databases using aerial / satellite data
--Generation of DEM/DTM and ortho-rectified aerial and satellite data 
Cadastral Mapping
--Map updation using high-resolution satellite data 

Complete Solutions
--Utility GIS
--Close contour mapping and DTM generation using LIDAR data
--Alignment studies for canal/road/railways
--Cut and fill volume estimation – Volumetric analysis
--L-section, cross-section profile generation
--Power-line monitoring and maintenance
--3-D city modeling and visualization

Aerial Camera
AS&DMA has two digital cameras, Vexcel’s ULTRACAM-D Large Format Digital camera and Enerquest’s medium format camera with CCD pixel dimension of 9 µm. With the Large Format Digital Camera a resolution of upto 3 cm can be achieved. Large Format digital Camera(LFDC) A Large Format Digital Camera, Ultracam-D has been inducted and operationalized. It is a frame camera with 11500 x 7500 pixels with pixel size of 9 µm and a geometrical accuracy of 2 µm. The major components of the system are Camera, Computer Controlled Navigation System (CCNS), Aero-control computer, GPS, Inertial Measurement Unit (IMU), three axis stabilized gyro mount.

Major Advantages of LFDC
-- Eliminates the film processing and scanning steps required in case of analog film. 
-- Provides PAN, Colour and NIR images 
-- Improved feature interpretation and automatic point matching possible due to true colour images. 
-- Direct georeferencing of images using GPS/IMU.

Airborne LiDAR
Airborne LiDAR AS&DMA has in its fold an Airborne LIDAR ALS50 System coupled with Enerquest’s medium format Digital Camera, GPS & IMU which enables simultaneous acquisition of LIDAR data for height information, images for Planimetric mapping purposes and GPS & IMU for direct georeferencing. IntroductionAirborne LIDAR is an active remote sensing system operating at 1064 nm and is used for generation of high accurate DEM/DTM generation at shorter TAT with an height accuracy of ±15cm. The multiple return technology of LIDAR helps to determine ground elevation even under trees and thick canopy.

LIDAR System
The airborne LIDAR is tightly integrated with an onboard Kinematic GPS and an Inertial Measuring Unit (IMU). GPS measures the position of the Aircraft every half-second and IMU measures the attitude of the laser sensor at the rate of 200 times per second, which helps in determining the principle position of the laser sensor, and in turn, the range of the objects from the sensor. The LIDAR unit is also integrated with the Digital Camera of 4K x 4K frame size, which is used to get the image. Also the digital video camera available along with the unit aids in the navigation and path recovery process to determine the accuracy of the flying as per planning.

Principle
The principle of operation is that the Laser scanner mounted in aircraft emits laser beams with high frequency and receives the reflected beam. The time difference between emission of laser beam and reception of the reflected laser signal is recorded to get the distance (range). GPS data recorded in air and on ground (DGPS base stations for every 25-40 kms) determine accurate aircraft position. The coordinates of the points on ground are calculated based on: 
--aircraft position (latitude/longitude/elevation) 
--aircraft orientation (roll/pitch/heading) 
--scan angle 
--round-trip propagation time of laser pulse 
--atmospherics

Applications
Canal alignment 
--Road alignment 
--Close contouring (0.5m interval) 
--Forest surveys 
--Flood plain mapping 
--Coastal geomorphology

Facilities
AS&DM is equipped with state-of-the-art survey equipment and expertise for providing high precision survey solutions required for KGPS-assisted photogrammetry, DGPS surveys for precise Ground control points and also for establishing national reference frame in WGS-84 coordinate system for national and international projects. 
--Establishment of GPS reference stations and operations 
--GPS assisted airborne surveys 
--DGPS based ground control surveys to collect precise GCPs for photogrammetric process 
--Precise leveling surveys for height control 
--Total Station surveys for detailed mapping 
--Surveys for establishing Antenna Centre Point (ACP) Position and Azimuth 
--Post processing and integrating with GIS database 
--Expertise in long baseline processing The survey equipment include geodetic quality dual frequency GPS receivers, mapping grade and hand held GPS receivers, digital levels and total station. Click here to view the list of the survey equipments. The GPS equipment is capable of logging data with various epoch rates facilitating data collection as per the project specifications. The data collected during the missions is processed using post processing tools.

Data Processing techniques
--DGPS processing to derive precise co-ordinates 
--Airborne GPS processing to derive Exposure station co-ordinates 
--GPS+IMU combined processing to derive precise EO parameters 
--PPP technique to derive precise co-ordinates in standalone mode using precise ephemeris and satellite clock files

Overview