Lecture 13.1: Airborne Lidar Systems

Transcription

1 Lecture 13.1: Airborne Lidar Systems

2 1. Introduction v The main advantages of airborne lidar systems are that they expand the geographical range of studies beyond those possible by surface-based fixed or mobile lidar systems by virtue of being able to fly to high altitudes and to remote locations. v The main disadvantage of using an airborne lidar is the complexity and cost of conducting aircraft operations, a fact that limits the number of airborne missions. v In the nadir direction, the atmospheric density increases with range r (decreasing altitude), compensating somewhat for the 1/r2 falloff in lidar signal with range. v For the zenith direction, the advantage is that the airborne lidar system is higher and thus closer to the atmosphere being measured. v The main disadvantage of using an airborne lidar is the complexity and cost of conducting aircraft operations, a fact that limits the number of airborne missions.

3 SPECIFIC REQUIREMENTS FOR AIRBORNE LIDAR v The primary constraints include limitations on size, mass, power, and receiver aperture, and the ability to operate in an environment with high- and lowfrequency vibrations and temperature and cabin pressure variations. v Should be designed and developed to function with limited operator intervention during flight. v To work in an eye-safe mode when flying over populated areas or in the vicinity of other aircraft.

4 Airborne lidar measurements of aerosols NASA s Global Tropospheric Experiment (GTE) GTE: Biosphere/Atmosphere Exchange: ABLE-Expeditions study of aerosols from biomass burning GTE Long Range Transport: TRACE-A and PEM-Expeditions Trace gases

5 NASA s Global Tropospheric Experiment (GTE)

6 NASA/GSFS Large Aperture Scanning Airborne Lidar (LASAL) A nadir viewing, scanning Nd:YAG-based lidar, The system operates at a wavelength of 1064 nm and includes a large (36 x 25 inch) mirror, having two axes of motion. capable of rendering a three-dimensional structure of the convective boundary layer and deriving optical thickness over large areas.

7 Airborne lidar measurements of wind Wind Infrared Doppler Lidar (WIND)

8

9

10

11 Airborne DIAL system NASA Langley s airborne UV DIAL system LASE (Lidar Atmospheric Sensing Experiment)

12 Airborne DIAL system

13 NASA Langley s airborne UV DIAL system

14 Airborne RESONANCE FLUORESCENCE LIDAR The University of Illinois Na airborne lidar flown in these campaigns. Hawaiian Airglow-90 (ALOHA-90) Campaign, 1990 ALOHA-93, 1993

15 NASA/GSFC and Langley s Airborne Raman Ozone, Aerosol, and Temperature Lidar (AROTEL) AROTEL has four primary data products: vertical profile of ozone between km vertical profile of temperature from 13 km to ~60 km vertical profile of aerosol scattering aerosol depolarization at 532 nm The transmitter in the AROTEL instrument comprises two different lasers: a XeCl excimer laser, transmitting 308 nm; and a Nd-YAG laser transmitting at 1064, 532, and 355 nm.

16 Lecture 13.2: Space-based lidar

17 Introduction v Technical requirements for space lidar are more demanding than for ground-based or airborne systems. The range to a target within the atmosphere is much larger, with orbital altitudes generally falling in the range of 250 to 700 km, so that R 2 losses are much larger. To increased lidar system photon sensitivity, use higher laser pulse energy and pulse repetition frequency (PRF), larger receiver collection area. However, satellite allocations for electrical power, instrument mass, telemetry, thermal control, etc. are limited. Design of a lidar to be operated on a satellite involves careful balancing of many different constraints. v Must be specially designed to survive the mechanical vibration loads of launch and operate in the vacuum of space v Must be designed to be highly reliable because they must operate without the need for repair or adjustment.

18

19 Technology development for Spacebased lidar missions v The Laser Risk Reduction and Active Optical Remote Sensing Programs v Lidar Technologies for Space Missions Laser Lidar Telescope Detector

20 The Laser Risk Reduction and Active Optical Remote Sensing Programs v Laser Risk Reduction Program (LRRP) was initiated by NASA in 2002 to develop technologies that ensure the successful development of the broad range of lidar missions envisioned by NASA. v Three key recommendations have been made by the LRRP team to advance the space laser technology developing two laser transmitters to provide the primary wavelengths for carrying out six priority measurements for Earth sciences, and chemical and biological agent detection for civilian and warfare applications. (Nd:YAG/YLF laser at 1.06mm and Ho:Tm:YLF/LuLiF laser at 2.05 mm) develop space-qualified laser diode arrays (LDAs) develop eye-safe spacebased solid-state laser transmitters for multiple lidar applications.

21 Lidar Technologies for Space Missions v Laser laser system ruggedness Crossed-Porro laser resonator designs Use as few optical components as possible Good mechanical and thermal design long lifetime operation. Operate all optical components at appropriately derated levels. Design the space laser with enough redundancy.

22 Lidar Technologies for Space Missions v Lidar Telescope high rigidity and long-term stability vs. fabrication cost and mass Fabrication of carbon/silicon carbide (C/SiC) mirrors Using metal alloy shells (next generation of space telescope). v Detector considerably higher sensitivity

23 Space-based lidar for observations of aerosols and clouds The Lidar In-space Technology Experiment (LITE) flew on the Space Shuttle STS-64 mission in September 1994 as a proof-of-concept demonstration

24

25 ICESat (aka: Laser Altimetry Mision) The Ice, Cloud, and Elevation Satellite v Geoscience Laser Altimeter System (GLAS) - sole instrument v Combinination surface lidar with dual wavelength cloud and aerosol lidar v Launched Jan 12, 2003 Jan 15, 2003 Earth pointing v Measures ice sheet elevations changes in elevation through time height profiles of clouds and aerosols land elevations vegetation cover approximate sea thickness. Images and info from

26 ICESat (aka: Laser Altimetry Mision) The Ice, Cloud, and Elevation Satellite v First laser-ranging instrument for continuous global observations of Earth v Mission data will be distributed and archived by the National Snow and Ice Data Center v More detailed info ICESat FACT SHEET (.pdf) ICESat BROCHURE (.pdf) ICESat LITHO (.pdf) Environmental Assessment for ICESat (.pdf) National Environmental Policy Act (.pdf) Images and info from

27 ICESat (aka: Laser Altimetry Mision) The Ice, Cloud, and Elevation Satellite v v More detailed info ICESat FACT SHEET (.pdf) ICESat BROCHURE (.pdf) ICESat LITHO (.pdf) Environmental Assessment for ICESat (.pdf) National Environmental Policy Act (.pdf) Images and info from

28 The Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) is the 2nd-generation of the orbiting laser altimeter ICESat scheduled for launch in late 2015 ICESat-2 ICESat_2.ppt

29 CALIPSO: Lidar on Satellite CALIPSO was Lunched in CALIPSO.ppt CALIPSO_summary.pdf