Instrument : High Spectral Resolution Lidar (HSRL)
High Spectral Resolution Lidar (HSRL) systems provide vertical profiles of optical depth, backscatter cross-section, depolarization, and backscatter phase function. All HSRL measurements are absolutely calibrated by reference to molecular scattering, which is measured at each point in the lidar profile. Like the Raman lidar but unlike simple backscatter lidars such as the micropulse lidar, the HSRL can measure backscatter cross-sections and optical depths without prior assumptions about the scattering properties of the atmosphere. The depolarization observations also allow robust discrimination between ice and water clouds. In addition, rigorous error estimates can be computed for all measurements. A very narrow, angular field of view reduces multiple scattering contributions. The small field of view, coupled with a narrow optical bandwidth, nearly eliminates noise due to scattered sunlight. There are two operational U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility HSRL systems, one at the Barrow North Slope of Alaska (NSA) site and the other in the second ARM Mobile Facility (AMF2) collection of instrumentation.
Description of Raw Data
The raw HSRL data are in NetCDF format and include four backscatter channels:
|molecular||=||molecular signal only|
These data are uncalibrated, but can be used to obtain a qualitative view of the atmospheric column. The file does not include a height variable, but the height can be calculated using the following expression:
delta_z (in meters) = binwidth_ns*(1.0e-9)*(3.0e8)/2.0
z (in meters) = ([0,1,2,3,...,bincount-1]-pulse_index)*delta_z
Where "binwidth_ns" and "pulse_index" are attributes of the four backscatter variables and bincount is the vertical dimension.
Note: the first several z values will be negative because the system records background data for a few nanoseconds before sending out the pulse.
To derive physical properties like optical extinction, the high and low gain channels will be merged to provide a unified aerosol+molecular profile and combined with the other channels. These higher order products will be available soon.
Shipley, ST, DH Tracy, EW Eloranta, JT Trauger, JT Sroga, FL Roesler and JA Weinman, "A High Spectral Resolution Lidar to measure optical scattering properties of atmospheric aersols, Part I: Instrumentation and theory" Applied Optics, 23, 3716 – 3724, 1983.
Piironen, P, and EW Eloranta, "Demonstration of a high spectral resolution lidar based on an iodine absorption filter," OL 19, 234 – 236, 1994.
Piironen, P, "A High Spectral Resolution Lidar Based on an Iodine Absorption Filter", Ph.D. Thesis, University of Joensuu, Department of Physics, 1994.
- hsrl : High Spectral Resolution Lidar
The following measurements are those considered scientifically relevant.