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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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In-Situ Measurements of Aerosol Optical Properties

Three instruments, a cavity ringdown (CRD) aerosol extinction spectrometer, a photoacoustic absorption spectrometer (PAS), and an ultra-high sensitivity aerosol size spectrometer (UHSAS) comprise the AOP package. The AOP package provides multi‐wavelength, multi-RH aerosol extinction and absorption measurements with fast response and excellent accuracy and stability on aircraft platforms. The instruments will also characterize the optics of black carbon (BC) mixing state, brown carbon, and water uptake of aerosol. Aerosol asymmetry parameter, needed for radiative transfer modeling, will be calculated from dry and humidified particle size distributions.

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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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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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