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Understanding Lidar for Resource Management
 Mudit Mathur 1341 S-2 RK Purum New Delhi-30 Email: mr.mudit@gmail.com  Jasbir Sandhu J3/79 Malviyanagar New Delhi-17 Email: jasbir-sandhu@myway.com 1. INTRODUCTION The biggest challenge in the modern remote sensing is to device an assured means to achieve a high degree of accuracy in ground sampling, without undertaking physical survey. This has been an enigma for the civil as well as military remote sensing scientists. LiDAR(Light Detection and Ranging; or Laser Imaging Detection and Ranging), is a technology that determines distance to an object or surface using laser pulses, the range to an object is determined by measuring the time delay between transmission of a pulse and detection of the reflected signals. The acronym LADAR (Laser Detection and Ranging) for elastic backscatter is mainly used in military context. The term laser radar is also in use but somewhat misleading as laser light and not radio waves are used. LiDAR, an airborne technique is becoming more and more important in terrain applications programmes and for acquiring remotely sensed topographical data. LiDAR term as defined in the dictionary say all about its physical property and its capability Main Entry: li•dar Pronunciation: 'Li -"där Function: noun Etymology: light + radar Definition-1: A device that is similar in operation to radar but emits pulsed laser light instead of microwaves Definition-2: A method of detecting distant objects and determining their position, velocity, or other characteristics by analysis of pulsed laser light reflected from their surfaces. The equipment are used in such detection. This article provides a window for understanding the few of many capabilities of the LiDAR that can be used in infinite application of resource management so that optimized canalization and exploitation of the resources can be attempted. In all we should not lose the sight of the fact that LiDAR is one of the sources of highly accurate data and not the solution by itself. Technology in a glance The LiDAR system basically consists of integration of three technologies, namely, Inertial Navigation System (INS), LASER, and GPS. A pulsed laser ranging system is mounted in an aircraft equipped with a precise kinematic GPS receiver and an Inertial Navigation System (INS). Solid-state lasers are now available that can produce thousands of pulses per second, each pulse having a duration of a few nanoseconds (109 seconds). The laser basically consists of an emitting diode that produces a light source at a very specific frequency. The signal is sent towards the earth where it is reflected off a feature back towards the aircraft. A receiver then captures the return pulse. Using accurate timing, the distance to the feature can be measured. By knowing a speed of the light and the time the signal takes to travel from the aircraft to the object and back to the aircraft, the distances can be computed. Using a rotating mirror inside the laser transmitter, the laser pulses can be made to sweep through an angle, tracing out a line on the ground. By reversing the direction of rotation at a selected angular interval, the laser pulses can be made to scan back and forth along a line. When such a laser ranging system is mounted in an aircraft with the scan line perpendicular to the direction of flight, it produces a saw tooth pattern along the flight path.  There are multitudinous usages of LiDAR technologies. Presently worldwide network of observatories use LiDAR to measure the distance of earth-moon with millimeter precision and enabling tests of general relativity. The Mars Orbiting Laser Altimeter [MOLA], used a LiDAR instrument in a Mars-orbiting satellite to produce a stunningly accurate topographic survey of the red planet. In atmospherics, LiDAR is used as a remote detection instrument to measure densities of certain constituents of the middle and upper atmosphere, such as potassium, sodium, or molecular nitrogen and oxygen. These measurements can be used to calculate temperatures. LiDAR can also be used to measure wind speed. One situation where LiDAR has notable non-scientific application is for vehicle speed measurement. The technology for this application is small enough to be mounted in a hand held camera "gun" and permits a particular vehicle's speed to be determined from a stream of traffic. Military applications are not yet in place, but a considerable amount of research is underway in their use for imaging. Their higher resolution makes them particularly good for collecting enough detail to identify targets, such as tanks. Here the name LADAR is more common. At the JET nuclear fusion research facility in Oxfordshire. LIDAR Thomson Scattering is used to determine Electron Density and Temperature profiles of the plasma. There are ongoing military research programmes in Sweden, Denmark, USA and UK with 3-D gated viewing imaging at several kilometers range with a range resolution and accuracy less than ten centimeters
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