Thursday, April 3, 2008

LIDAR INTRODUCTION

LIDAR (Light Detection and Ranging) is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser pulses. Like the similar radar technology, which uses radio waves instead of light, the range to an object is determined by measuring the time delay between transmission of a pulse and detection of the reflected signal. LIDAR technology has application in archaeology, geography, geology, geomorphology, seismology, remote sensing and atmospheric physics.Other terms for LIDAR include ALSM (Airborne Laser Swath Mapping) and laser altimetry. The acronym LADAR (Laser Detection and Ranging) is often used in military contexts. The term laser radar is also in use but is misleading because it uses laser light and not the radiowaves that are the basis of conventional radar.

The primary difference between lidar and radar is that with lidar, much shorter wavelengths of the electromagnetic spectrum are used, typically in the ultraviolet, visible, or near infrared. In general it is possible to image a feature or object only about the same size as the wavelength, or larger. Thus lidar is highly sensitive to aerosols and cloud particles and has many applications in atmospheric research and meteorology. An object needs to produce a dielectric discontinuity in order to reflect the transmitted wave. At radar (microwave or radio) frequencies, a metallic object produces a significant reflection. However non-metallic objects, such as rain and rocks produce weaker reflections and some materials may produce no detectable reflection at all, meaning some objects or features are effectively invisible at radar frequencies. This is especially true for very small objects (such as single molecules and aerosols). Lasers provide one solution to these problems. The beam densities and coherency are excellent. Moreover the wavelengths are much smaller than can be achieved with radio systems, and range from about 10 micrometers to the UV (ca. 250 nm). At such wavelengths, the waves are "reflected" very well from small objects. This type of reflection is called backscattering. Different types of scattering are used for different lidar applications, most common are Rayleigh scattering, Mie scattering and Raman scattering as well as fluorescence. The wavelengths are ideal for making measurements of smoke and other airborne particles (aerosols), clouds, and air molecules. A laser typically has a very narrow beam which allows the mapping of physical features with very high resolution compared with radar. In addition, many chemical compounds interact more strongly at visible wavelengths than at microwaves, resulting in a stronger image of these materials. Suitable combinations of lasers can allow for remote mapping of atmospheric contents by looking for wavelength-dependent changes in the intensity of the returned signal. Lidar has been used extensively for atmospheric research and meteorology. With the deployment of the GPS in the 1980's precision positioning of aircraft became possible. GPS based surveying technology has made airborne surveying and mapping applications possible and practical. Many have been developed, using downward-looking lidar instruments mounted in aircraft or satellites. A recent example is the NASA Experimental Advanced Research Lidar.

LIDAR RESOURCES

LAStools Tools page from Martin Isenburg and Jonathan Shewchuk for converting, viewing, and compressing LIDAR data in LAS format.

LIDAR Data from NOAA Use this page to see if LIDAR data is available for download from NOAA within the United States.

LIDAR Data Handler NOAA Coastal Services Center ArcView 3.x and ArcMap extensions for manipulating LIDAR data.

LIDAR data processing with open source tools Blog post from Matt Perry on the availability of open source tools for processing LIDAR data. Included in the post is a link to the pylas.py module.

LIDAR Use in a GIS Resource page from NOAA on using LiDAR data in GIS. Some of the information is outdate with references to ArcView 3.x project files but there are some useful tools available on the site.

Visualizing LIDAR in Google Earth Created by Martin Isenburg and Jonathan Shewchuk, this tool allows for the ” quick visualization of LIDAR data in Google Earth.”

Courtesy: www.gislounge.com/lidar-resources

RADAR RESOURCES

Title

Description

Author

SAR Polarimetry Tutorial

This tutorial is for the undeterred reader who really wants (or has to) actually use polarimetry for SAR applications. It covers most aspects of SAR polarimetry (i.e. wave polarization, polarimetric description of scatterers, target decomposition, applications, etc.).

Martin Hellmann

Fuzzy Logic Introduction

Brief and basic introduction to the concept of fuzzy theory illustrated with an example (fuzzy classification of fully polarimetric SAR data)

Martin Hellmann

Synthetic Aperture Radar - Basic Concepts and Image Formation

Introduction in the image formation process and basic concepts of synthetic aperture radar. Includes also some practical exercises (processing of a small SAR raw data set).

Andreas Reigber

SAR Interferometry - An Introduction

Presentation made for the TMR SAR interferometry workshop held in Rennes/France 03.-07. April 2001. Its tries to outline the way from a conventional SAR image to a digital elevation model.

Andreas Reigber

Polarimetry for dummies

This tutorial is meant to give the interested reader with a limited or no previous knowledge about waves and polarimetry an introduction into the field and the terminology of waves and polarimetry.

Martin Hellmann

External Tutorials:

Title

Description

Author

Fundamentals of Remote Sensing

A mix of several tutorials and links to related information with strong focus on SAR and SAR interferometry. Lots of useful information.

D.J Kim

Radar and Microwave Remote Sensing

Chapter 8 of NASA's Remote Sensing Tutorial. A little bit old-fashioned overview about information content and interpretation of SAR images.

Nicholas M. Short (NASA)

Radar and Steroscopy

This very nice tutorial touches on relevant aspects of stereoscopy and radar remote sensing, with special focus on the use of RADARSAT imagery.

Dr. Thierry Toutin and Corinna Vester (Canada Centre for Remote Sensing

Scientific SAR User's Guide

This document is intended to provide an introduction and background to scientists wishing to interpret SAR image data. The coverage is necessarily brief but thorough references and citations are provided for the user who wishes to pursue the subject in greater depth.

Coert Olmsted (Alaska Satellite Facility)

SAR FAQ

Frequently Asked Questions to SAR, what to say more.

Alaska Satellite Facility

Online Microwave Antenna Book

An Online Microwave Antennabook

Paul Wade

Offtopic:

Title

Description

Author

Physics Formulary

This document contains 108 pages of the most important formulas in physics. It is intended to be a short reference for anyone who works with physics and often needs to look up equations.

J.C.A. Wevers

Internet Mathematics Library

Everything you never wanted to know about mathematics.

The Math Forum

Courtesy: www.epsilon.nought.de

LINKS FROM EPSILON NOUGHT

Open remotesensing sites

  • remotesensing.org: This site is dedicated to making Remote Sensing algorithms, code, and technology available to all interested parties. Resources are provided to facilitate communication and development of open source tools. It is hoped that this effort will attract participation from companies, students, professors, and agencies that are involved in remote sensing efforts. Through the combination of our collective efforts all parties will benefit through the development of new capabilities, tools, and advances in this field.

  • The Alaska Satellite Facility: The Alaska Satellite Facility (ASF) is located in the Geophysical Institute (GI) on the Fairbanks campus of the University of Alaska (UAF). ASF is a satellite-tracking ground station for the acquisition, processing, archiving and distribution of Synthetic Aperture Radar (SAR) imagery and derived products for the science community in cooperation with international flight agencies. Lots of tools, and information on SAR.

Open software sites

  • netlib.org: The Netlib repository contains freely available software, documents, and databases of interest to the numerical, scientific computing, and other communities. The collection is automatically worldwide synchronized, to provide reliable and network efficient service to the global community. At this place you can find numerical libraries for many purposes, and if you are clever and don't want to program everything from the beginning, you should have a look.

  • The GNU Scientific Library: The GNU Scientific Library (GSL) is a collection of routines for numerical computing. The routines are written from scratch by the GSL team in ANSI C, and are meant to present a modern Applications Programming Interface (API) for C programmers, while allowing wrappers to be written for very high level languages.

  • freegis.org: Here, links to free GIS tools and geographic data are collected. Many proprietary applications can now be substituted by a free solution. Unfortunately the development for some software sectors have been slightly neglected. We worked with GIS and geographic data for several years and permanently fought with unsatisfactory proprietary tools. Even more problematic for Europe is the availability of geographic data. All over the internet we did not find a site dedicated to freedom concerning GIS and geographic data. Well, now there is one.

  • ERS SAR Toolbox: The ERS SAR Toolbox (ERS STBX) is a collection of software tools which has been developed to help the remote sensing community to use ERS SAR data. The purpose of the Toolbox is not to duplicate existing commercial packages, but to complement them with functions dedicated to the handling of ESA ERS SAR products. The Toolbox contains tools to perform functions like: data extraction, quick look generation, calibration and radiometric correction, co-registration and speckle filtering. It can be used on the many platforms (PC, Mac, Sun, etc.) and can be used to handle most ERS SAR products (PRI, SLC, SLCI, etc.) generated within the ESA ERS ground segment and at receiving stations round the world.

  • Ellipse SAR Geocoding Software: This software, supplied as an IDL .SAV file, allows the automated ellipsoid correction of an ERS SAR PRI image using a full range doppler solution. Such a solution is more accurate than warping using corner coordinates and is fully automated. The results should be within 25m (2 pixels) of error.

Courtesy: www.epsilon.nought.de

RADAR TUTORIALS

Andraka Consulting Group FPGAs Make a Radar Signal Processor on a Chip a Reality (PDF, 66Kb) This paper describes how we perform over 10 billion multiplications per second in one FPGA. The secret is distributed arithmetic, and this paper tells you how it is done. It also addresses digital demodulation and matched filtering in FPGAs.

Design and Demonstration of an Advanced On-Board Processor for the Second-Generation Precipitation Radar (PDF, 4126Kb) This paper discusses the application of the radar processor described in the paper "FPGAs make a radar signal processor on a chip a reality". Lots of colorful graphics, hence the large size.

Goddard Space Flight Center Remote Sensing Tutorial Overview, Radar and Microwave Remote Sensing, How Radar Works, ...
GRORADAR Ground Penetrating Radar Radar is an acronym coined in the 1934 for RAdio Detection And Ranging. The first ground penetrating radar survey was performed in Austria in 1929 to sound the depth of a glacier (Stern, 1929, 1930). The technology was largely forgotten (despite more than 36 patents filed between 1936 and 1971 that might loosely be called subsurface radar) until the late 1950's when U.S. Air Force radars were seeing through ice as planes tried to land in Greenland, but misread the altitude and crashed into the ice. This started investigations into the ability of radar to see into the subsurface not only for ice sounding but also mapping subsoil properties and the water table...
DARTS (Digital Amateur Rocket Tracking System) Building Your Own Amateur Radar Some years ago, amateur radio hobbyists wouldn't have dreamed of building or owning their own radar system because of the incredibly high costs of microwave components. Thanks in part to the explosions in cellular phone usage, consumer GPS and satellite TV, microwave components covering up to Ku band are now readily available at low cost. In addition, amateur radar types have all the military and commercial radar surplus to draw upon, and many other nontraditional resources as well.
Igence TWP Tutorials General introduction, Differential and integral calculus, Matrices and vectors, Fourier transforms, Special functions, Probability and random processes, Detection and discrimination, Clutter modelling and analysis, Clutter simulation techniques, Contour integration and Lagrange multipliers
Sandia National Laboratories Synthetic Aperture Radar What is Synthetic Aperture Radar?, How does Synthetic Aperture Radar work?, SAR Applications, ...
UIUIC DAS Radar Meteorology: online remote sensing guide Radars have an important role in the field of meteorology. These devices send out and receive signals providing valuable information about the location and intensity of precipitation. Advanced Doppler radar technology goes beyond simple detection to providing high resolution reflectivity and estimated velocity data, which is vital to short term forecasting and severe weather prediction. The purpose of this module is to introduce the basics of radar meteorology, features of WSR-88D and MDR radar imagery, and how to interpret Doppler velocity patterns.
WeatherTAP.com Radar Tutorial Radar Background, What is Radar?, What is Doppler Radar?, What is NEXRAD Radar?, Understanding NEXRAD Operation Scanning Patterns (VCPs), Operating Modes, Clear Air Mode, ...
Courtesy: www.palowireless.com/radar/tutorials.asp
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MORE TO COME..,