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High Spectral Resolution Lidar 2

The NASA Langley airborne High Spectral Resolution Lidar 2 (HSRL) is used to characterize clouds and small particles in the atmosphere, called aerosols. From an airborne platform, the HSRL2 scientist team studies aerosol size, composition, distribution and movement.
 

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Multicenter Airborne Coherent Atmospheric Wind Sensor

MACAWS is an airborne side-scanning Doppler laser radar (lidar) which measures two dimensional wind fields, vertical wind profiles, and aerosol backscatter from clear air and clouds. Range varies from 10-30 km depending on aerosol abundance and cloud attenuation. Upon exiting the aircraft, the lidar beam is completely eye-safe. MACAWS is developed and operated cooperatively by the atmospheric lidar remote sensing groups of NASA Marshall Space Flight Center, NOAA Environmental Technology Laboratory, and Jet Propulsion Laboratory.

MACAWS consists of: a frequency-stable pulsed transverse-excited atmospheric pressure carbon dioxide laser emitting 0.5-1.0 J per pulse at 10.6 micron wavelength at a nominal pulse repetition frequency (PRF) of ~20 Hz; a coherent receiver employing a cryogenically-cooled HgCdTe detector; a 0.3 m off-axis paraboloidal telescope shared by the transmitter and receiver in a monostatic configuration; a ruggedized optical table and three-point support structure; a scanner using two counter-rotating germanium wedges to refract the transmitted beam in the desired direction; an inertial navigation system (INS) for frequent measurements of aircraft attitude and speed; data processing, display, and storage devices; and an Operations Control System (OCS) to coordinate all system functions.

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Differential Absorption Lidar

The NASA Langley Airborne Differential Absorption Lidar (DIAL) system uses four lasers to make DIAL O3 profile measurements in the ultraviolet (UV) simultaneously with aerosol profile measurements in the visible and IR. Recent changes incorporate an additional laser and modifications to the receiver system that will provide aerosol backscatter, extinction, and depolarization profile measurements at three wavelengths (UV, visible, and NIR). For SEAC4RS, the DIAL instrument will include for the first time aerosol and cloud measurements implementing the High Spectral Resolution Lidar (HSRL) technique [Hair, 2008]. The modifications include integrating an additional 3-wavelength (355 nm, 532 nm, 1064 nm) narrowband laser and the receiver to make the following measurements; depolarization at all three wavelengths, aerosol/cloud backscatter and extinction at 532 nm via the HSRL technique, and aerosol/cloud backscatter at the 355 and 1064 nm via the standard backscatter lidar technique. Integration of the aerosol extinction profile at 532nm above and below the aircraft also provides aerosol optical depth (AOD) along the aircraft flight track.

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High Spectral Resolution Lidar

The NASA Langley airborne High Spectral Resolution Lidar (HSRL) is used to characterize clouds and small particles in the atmosphere, called aerosols. From an airborne platform, the HSRL scientist team studies aerosol size, composition, distribution and movement.

The HSRL instrument is an innovative technology that is similar to radar; however, with lidar, radio waves are replaced with laser light. Lidar allows researchers to see the vertical dimension of the atmosphere, and the advanced HSRL makes measurements that can even distinguish among different aerosol types and their sources. The HSRL technique takes advantage of the spectral distribution of the lidar return signal to discriminate aerosol and molecular signals and thereby measure aerosol extinction and backscatter independently.

The HSRL provides measurements of aerosol extinction at 532 nm and aerosol backscatter and depolarization at 532 and 1064 nm. The HSRL measurements of aerosol extinction, backscattering, and depolarization profiles are being used to:

1) characterize the spatial and vertical distributions of aerosols
2) quantify aerosol extinction and optical thickness contributed by various aerosol types
3) investigate aerosol variability near clouds
4) evaluate model simulations of aerosol transport
5) assess aerosol optical properties derived from a combination of surface, airborne, and satellite measurements.

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B-200 - LARC, DC-8 - AFRC, NASA P-3 Orion - WFF
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Doppler Aerosol WiNd Lidar

The NASA Langley Research Center DAWN (Doppler Aerosol WiNd) lidar system employs a pulsed, solid-state laser operating at 2053 nm wavelength. It pulses at 10 Hz with up to 100 mJ/pulse which are 180 ns long. Using a wedge scanner, several different azimuth angles can be measured below the aircraft, all at a 30 degree off-nadir angle. Multiple azimuth angles enable horizontal wind calculation, mitigate cloud obscurations, and measure atmospheric variability. DAWN can provide vertical profiles of the zonal (u) and meridional (v) components of the horizontal wind below the aircraft, typically at ~60 meter resolution. Various vertical and horizontal resolutions are possible in post processing. DAWN can also provide vertical profiles of line of sight (LOS) wind speed at each azimuth angle. It can also be operated to stare persistently at any particular azimuth angle to simulate what a satellite such as European Space Agency Atmospheric Dynamics Mission (ADM) Aeolus would observe. DAWN signal returns also permit retrieval of vertical profiles of relative aerosol backscatter and wind turbulence.

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Lidar Atmosphere Sensing Experiment

The Differential Absorption Lidar uses the backscatter of two simultaneous laser wavelengths through zenith and nadir windows to measure the vertical profiles of H2O and aerosols/clouds.

NASA's Lidar Atmospheric Sensing Experiment (LASE) system is an airborne DIAL (Differential Absorption Lidar) system used to measure water vapor, aerosols, and clouds throughout the troposphere. LASE probes the atmosphere using lasers to transmit light in the 815-nm absorption band of water vapor. Pulses of laser light are fired vertically below the aircraft. A small fraction of the transmitted laser light is reflected from the atmosphere back to the aircraft and collected with a telescope receiver. The received light indicates the amount of water vapor along the path of the laser beam.

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Syed Ismail (Prev PI)

Aerosol Lidar

The Aerosol Lidar system measures profiles of aerosol and/or cloud backscatter at 532 and 1064 nm and aerosol/cloud depolarization at 532 nm. Backscatter profiles at these two wavelengths provide information on the relative concentration and spatial distribution of aerosol/cloud particles. Comparison of aerosol/cloud backscatter at the two wavelengths provides some indication of particle size. Measurement of the depolarizing effect of the particles (that is, the degree to which the polarization of the backscattered light from the particles differs from the linear polarization of the transmitted laser light) provides an indication of particle phase.

The Aerosol Lidar is a piggy-back instrument on AROTEL lidar fielded by John Burris and Tom McGee of NASA Goddard Space Flight Center. The light source for the aerosol measurements is a Continuum 9050 Nd:YAG laser operating at 50 shots per second. The laser transmits approximately 600 mJ at 1064 nm, 250 mJ at 532 nm, and 350 mJ at 355 nm. AROTEL also employs an excimer laser transmitting at 308 nm and uses the molecular and Raman backscatter from the 355 and 308 beams to measure ozone and temperature. Backscattered light at all wavelengths is collected by a 16-inch diameter Newtonian telescope with a selectable field stop. In the aft optics assembly following the telescope and field stop, the UV signals are separated from the 532- and 1064-nm signals by a dichroic beam splitter. The UV signals are directed to the AROTEL receiver assembly and the 532- and 1064-nm signals are directed to the Aerosol Lidar receiver assembly. In the Aerosol Lidar receiver, a rotating shutter blocks the very strong near-range 532- and 1064-nm signals in order to reduce distortion in the relatively weaker signals from higher altitudes. The 532- and 1064-nm signals are separated by a dichroic beam splitter and the 532-nm signal is further separated into orthogonal polarization components using a polarizing beam cube. A computer-controlled half-wave plate in front of the polarizing beam cube is rotated so that the polarization of the 532 signals are parallel and perpendicular to the polarization of the transmitted laser pulses. The signals at both wavelengths and both 532-nm polarizations are transmitted to detectors at the Aerosol Lidar data acquisition rack via fiber optic cables. Each optical signal, the 1064-nm total backscatter and the 532-nm parallel and perpendicularly polarized backscatter, is directed to two separate detectors, with 10% going to one detector and 90% to the other, in order to more accurately measure the signals over their full dynamic range. The 532-nm returns are measured with photo-multiplier tubes and the 1064-nm returns are measured with avalanche photo-diodes. Because of the high optical signal levels, all data are acquired in analog mode, using 12-bit analog-to-digital converters. The instrument operates under both daytime and nighttime lighting conditions, with a slight degradation in data quality during the daytime.

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Raman Airborne Spectroscopic Lidar

The Raman Airborne Spectroscopic Lidar (RASL) consists of a 15W ultraviolet laser, a 24-inch (61-centimeter) diameter Dahl-Kirkham telescope, a custom receiver package, and a structure to mount these components inside an aircraft. Both the DC-8 at NASA Dryden and the P-3 at NASA/Wallops are aircrafts that could carry RASL. The system is unique because it requires the largest window ever put into either of these aircraft. A fused-silica window, diameter of 27 inches (68.6 centimeters) and 2.375 inches (6 centimeters) thick is needed to withstand the pressure and temperature differentials at a 50,000-foot (15.2-kilometer) altitude.

In June through August of 2007, RASL flew numerous times on board a King Air B-200 aircraft out of Bridgewater, VA, in support of the 2007 Water Vapor Validation Experiments (WAVES) campaign. The WAVES campaign was a series of field experiments to validate satellite measurements. RASL data, along with data from ground-based and balloon-borne instruments, were used to assess the CALIPSO and TES instruments and for studies of mesoscale water vapor variability. During the test flights, RASL produced the first-ever simultaneous measurements of tropospheric water vapor mixing ratio and aerosol extinction from an airborne platform.

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Aerosol Optical Properties

Aerosols (particulate matter) have a dramatic effect on radiative forcing of the climate, in some cases cooling and in other cases warming. The Fourth Assessment Report of the IPCC estimates that direct radiative forcing due to all aerosols is a cooling of -0.50 W m-2 with absorbing aerosol (black carbon) responsible for a warming of +0.22 W m-2, but the uncertainties associated with these numbers are very large. Better measurements of the optical properties of aerosols, especially absorption coefficient and asymmetry parameter, and their spatial and temporal distribution are required to reduce these uncertainties and improve the ability of models to predict climate change. Aero3X was designed to provide such measurements. It is a light weight (11 kg), compact (0.25 x 0.30 x 0.6 m), and fast (1 Hz sample rate) instrument intended for use on an Unmanned Aerial System (UAS) but suitable for flight on other aircraft and for surface measurements. Aero3X uses an off-axis cavity ring-down technique to measure extinction coefficient and a reciprocal nephelometry technique for measurement of total-, forward- and back-scatter coefficients at wavelengths of 405 nm and 675 nm. Its outstanding precision (0.1 Mm-1) and sensitivity (0.2 Mm- 1) allow the determination of absorption coefficient, single-scattering albedo, estimates of backscatter to extinction ratio and asymmetry parameter at both wavelengths, and Angstrom exponent. Together with its humidification system for measurement of the dependence of aerosol optical properties on relative humidity, these represent a complete set of the aerosol optical properties important to climate and air quality. Aero3X was designed to operate in pollution plumes where NO2 may cause interference with the measurement, therefore, a measurement of NO2 mixing ratio is also made.

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Airborne Raman Ozone, Temperature, and Aerosol Lidar

This is a stratospheric lidar which is configured to fly on the NASA DC-8. It is a zenith viewing instrument, which makes vertical profile measurements of ozone, aerosols and temperature. Stratospheric ozone can be measured at solar zenith angles greater than ~30 degrees, while temperature and aerosols require SZA > 90 degrees. The SNR is maximized under dark coonditions. The measurement of Near-field water vapor measurements is being investigated and could be readily implemented. The instrument utilizes a XeCl excimer laser and a Nd-YAG laser to make DIAL, Raman DIAL, and backscatter measurements. A zenith viewing 16" telescope receives the lidar returns.

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