"RLPROFMR" VAP Process
Instrument Categories: Atmospheric Profiling, Derived Quantities and Models
Description: Raman LIDAR Vertical Profiles of Water Vapor Mixing Ratio
The primary goal of this VAP is to derive calibrated water vapor mixing ratio profiles from the Raman lidar at the SGP site. The VAP processes both the wide field-of-view (low altitude) and narrow field-of-view (high altitude) raw backscatter data, applying corrections for conflicts in laser/detector field-of-view (overlap) and differential transmission due to both molecules and aerosols. For each averaging interval, these two profiles are merged into a single profile, which is then multiplied by a height-independent calibration which is constant for the entire day. This calibration constant is derived from either the microwave radiometer (the default) or the 60 meter tower (used if the microwave calibration could not be performed for some reason). Data from three consecutive nighttime periods (the current day and the day before and after) are used in the determination of this factor. Factors which would prevent the calibration to the microwave radiometer include pervasive clouds (i.e., the lidar is unable to profile the entire column) or incomplete or missing pressure profiles (which are used in the calculation of total precipitable water vapor from the mixing ratio profiles).
In addition to a calibrated water vapor mixing ratio profile, temperature and pressure profiles are read in from either the AERI+GOES retrievals (the default) or radiosondes and these profiles are interpolated to the Raman lidar altitudes and sample times. These profiles are then used to compute coincident profiles of relative humidity. The water vapor profiles from these other profiling techniques is also used to estimate the fraction of the precipitable water vapor sensed by the Raman lidar during the daytime, since the increased background levels restricts the range the lidar can profile to approximately 3 km (during the nighttime, the lidar typically profiles beyond 8 km). This unitless estimate is used to compute the lidar's integrated water vapor profile into an estimate of total precipitable water vapor in the column.
For more information, see the Raman Lidar Profiles - Mixing Ratio.
Primary Measurements
The following measurements are those considered scientifically relevant. Refer to the datastream (netcdf) file headers for the list of all available measurements, including those recorded for diagnostic or quality assurance purposes.
