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Level 1b Cloudnet product:

Liquid water path (radiometer/lidar/model method)

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Summary

Designation
lwp-synergy
Level
1b
Algorithm design/Product maintainer
Institute
University of Reading
Description
This product contains the vertically integrated liquid water content, or liquid water path (lwp), obtained using dual-wavelength microwave radiometer, lidar and information from a forecast model. The lwp is assumed to be proportional to microwave optical depth, and the coefficients used to derive it are obtained as follows. For the liquid water coefficients, the lidar is used to locate the cloud and the model to diagnose cloud base temperature. The water vapour coefficients are derived from model temperature and vertical humidity distribution. Note that humidity is not used in an absolute sense but only in the sense of determining the effective emission temperature of a given water vapour path. Finally, periods of clear sky identified by lidar are used to estimate calibration errors in the radiometers using the fact that lwp retrieved in these regions should be zero. The lwp retrieved is therefore considerably more accurate (particularly at low lwp) than values obtained using fixed "climatological" coefficients.
Documentation
http://www.met.rdg.ac.uk/radar/documentation/
Relevant publication(s)
Pending
Quicklooks
http://www.met.rdg.ac.uk/radar/cloudnet/quicklooks/
Suggested acknowledgement
We acknowledge the Cloudnet project (European Union contract EVK2-2000-00611) for providing the liquid water path data, which was produced by the University of Reading using measurements from [SITE].

Dataset contents

Sample NetCDF file: 20030602_palaiseau_microwave-radiometer-lwp.nc
Header of sample NetCDF file in ASCII: 20030602_palaiseau_microwave-radiometer-lwp.cdl

The following is a description of the variables in this product, produced automatically from the metadata in the sample file (using the nc2html unix utility):

Dataset title: Liquid and vapour vater path from the palaiseauMicrowave Radiometers

    Institution:
    Data processed at the University of Reading,UK : http://www.met.reading.ac.uk
    References:Documentation may be found at: http://www.met.reading.ac.uk/radar/cloudnet/documentation/
    For further any further information about the retrieval technique using model and lidar, please contact Nicolas Gaussiat

Dimensions and coordinate variables

time
Time UTC
    Units:hours since 2003060200:00::00 +00:00
    Type:single-precision floating-point vector
radiometer_frequency
Radiometer frequency
    Units:GHz
    Type:single-precision floating-point vector

Variables

altitude
Height of ground level above mean sea level (Ordonance Survey Great Britain)
    Units:m
    Type:single-precision floating-point scalar
latitude
    Units:degrees_north
    Type:single-precision floating-point scalar
longitude
    Units:degrees_east
    Type:single-precision floating-point scalar
brightness_temperature(time, radiometer_frequency)
Microwave radiometer brightness temperature
    Units:K
    Type:single-precision floating-point array
lwp(time)
Liquid water path

    This variable is the vertically integrated liquid water content, or liquid water path (lwp), obtained using dual-wavelength microwave radiometer, lidar and information from a forecast model. The lwp is assumed to be proportional to microwave optical depth, and the coefficients used to derive it are obtained as follows. For the liquid water coefficients, the lidar is used to locate the cloud and the model to diagnose cloud base temperature. The water vapour coefficients are derived from model temperature and vertical humidity distribution. Note that humidity is not used in an absolute sense but only in the sense of determining the effective emission temperature of a given water vapour path. Finally, periods of clear sky identified by lidar are used to estimate calibration errors in the radiometers using the fact that lwp retrieved in these regions should be zero.

    Units:g m-2
    Type:single-precision floating-point vector
vwp(time)
Vapour water path

    This variable is the vertically integrated vapour water content, or vapour water path obtained using dual-wavelength microwave radiometer, lidar and information from a forecast model. The vwp is assumed to be proportional to microwave optical depth, and the coefficients used to derive it are obtained as follows. For the liquid water coefficients, the lidar is used to locate the cloud and the model to diagnose cloud base temperature. The water vapour coefficients are derived from model temperature and vertical humidity distribution. Note that humidity is not used in an absolute sense but only in the sense of determining the effective emission temperature of a given water vapour path. Finally, periods of clear sky identified by lidar are used to estimate calibration errors in the radiometers using the fact that lwp retrieved in these regions should be zero.

    Units:g m-2
    Type:single-precision floating-point vector
lwp_fixedcoefs_nolidar(time)
Liquid water path using fixed coefficients

    This variable is the vertically integrated liquid water content, or liquid water path obtained using dual-wavelength microwave radiometer. The lwp is assumed to be lineary related to the brightness temperatures. Fixed coefficients are determined by appling a bilinear fit over 2 years of model data

    Units:g m-2
    Type:single-precision floating-point vector
vwp_fixedcoefs_nolidar(time)
Vapour water path using fixed coefficients

    This variable is the vertically integrated vapour water content, or vapour water path (vwp), obtained using dual-wavelength microwave radiometer. The vwp is assumed to be lineary related to the brightness temperatures. Fixed coefficients are determined using a 2-year radiosonde ascent data set

    Units:g m-2
    Type:single-precision floating-point vector
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