| Description: | DQR No: Platform: SGPSONDEC1
Subject: CF Sonde Ground Check Corrections
Date Submitted: 11/8/94
Submitted By: Barry Lesht _X_ Instrument Mentor
___ EST Member
___ Science Team Member
___ Other _____________________________
For questions or problems, please contact the ARM Experiment Center at
509-375-6898 or via email at dqr@arm.gov.
Platform/Measurement: sgpsondec1
What level data: (raw,a0,a1,b1,c1 etc): all
What location was the data collected at: SGP/CF
Period of time in question
Begin Date 01/21/93 Time 16:40 (GMT)
End Date 08/03/94 Time 14:30 (GMT)
Data should be labeled:
_?_ questionable ___ All data fields affected
___ incorrect _X_ Only some data fields affected
___ wrong calibration
___ others
Discussion of Problem:
Between 1/21/93 and 8/3/94 all radiosondes launched from the central
facility were ground checked before launch. The ground check procedure
consists of placing the sonde sensor arm into a sealed, dessicated chamber
containing a certified calibrated mercury thermometer, allowing the sonde
to equilibrate, and comparing the sonde output readings for RH and
temperature to the thermometer reading and an assumed 0% RH. All data after
launch were "corrected" to account for any differences between the sonde
output and the reference conditions in the ground check set.
Analysis of the population of ground check values shows that the average
RH correction was 0% RH and average temperature correction was -0.4 degC.
Because there is some question as to whether applying the ground check
correction increases or decreases the accuracy of the output data, some
investigators may wish to remove the effect of the ground check before
using the data in their analyses. Ground checks were suspended on 8/3/94.
The algorithms for removing the ground check are:
RH (without ground check) = RH (as reported) - humidity_correction
Temp (without ground chk) = [Temp (as reported) - FACTOR1]/FACTOR2 where
FACTOR1 = [(90*temperature_correction)/(tref+90)
FACOTR2 = [1+(temperature_correction)/(tref+90)
The variables "humidity_correction" and "temperature_correction" are
metadata contained in the netCDF data files from 5/20/93 to 8/3/94.
Between 1/21/93 and 5/20/93 these variables were misnamed and are not
easily accessible via FORTRAN (see PIF 940917.1).
The variable tref is the actual temperature reported by the radiosonde
while in the ground check set. This variable is not included in the
netCDF file and can be estimated by using a value of 15 degC. The
correction function is relatively insensitive to variations in this
value. (see PIF 940917.2)
FORTRAN routines for reading the metadata and for applying the algorithms
to produce "uncorrected" data are available from the instrument mentor.
Other observations/measurements impacted by this problem:
Suggested Corrections of the Problem: (e.g. change calibration factor and
recompute, flag data with this comment, etc.)
Send (another) notice to users of the data.
Data Processing Notes Date |