| Description: | Background: After installation of the latest software update , we began performing formal
ground checks on RS92 radiosondes. By comparing the
radiosonde readings with reference values in a controlled environment, the
ground check is intended to ensure that the radiosonde sensors are in
calibration before launch. The radisonde values during the ground check
process are recorded automatically; the reference values are entered by the
operator. If the radiosonde readings vary from the reference values, the
system 'corrects' the radiosonde values. In the case of RH, the correction
is applied as an offset (true RH = indicated RH + correction).
Problem: Some operators misunderstood the ground-check procedure and entered the
radiosonde values of RH rather than the reference value (assumed 0%RH), thus, some soundings done
during this period have RH values that are different from what they would be if the
ground check procedure had been done correctly.
Consequence: Because the RH corrections generally are small (averaging
about 0.5% RH) and the precision of the reported RH data during this time
period is 1% RH, some values will not be affected at all; others will be off by about 1%
RH (still within the stated accuracy of the sensor).
Furthermore, because entering the radiosonde value as the reference value
results in a near zero 'correction,' one may view these soundings as being
done without the ground check correction. Also note that the dew point
value will be suspect as well.
I am attaching below a listing of the soundings that were affected during the indicated
time period. Users can see the magnitude of the problem and choose whether or not to apply
an offset in RH. Note that application of the offset to the processed RH data (in the
netCDF file) will not have the same effect of applying the correction to the absolutely
raw data (before processing), but the differences should be insignificant. Also note that
the corrections for each sounding are included in the netCDF header information. These
attributes are named 'humidity_correction' and 'humidity_correction_2'. The values of RH
indicated by the radiosonde while it is in the ground check set are in attributes
'humidity_gc_sonde' and 'humidity_gc_sonde_2.' There is an RH reading for each of the two RH
sensors used in the RS92 radiosonde.
Here is the list - RH1 and RH2 are the radiosonde readings in the ground
check set. Ref is the reference value entered by the operator. The
correcte reference value should be 0%. To obtain an approximation to the RH value that
would have been recorded if the ground check had been done
properly, subtract the Ref value from the indicated RH.
YYYYMMDD HHMM SerialN RH1 RH2 Ref
20060827 2332 B2624322 1.00 1.00 1.00
20060828 1731 B2634078 1.00 1.00 1.00
20060828 2332 B2624380 3.00 3.00 2.00
20060909 2331 B2615266 1.00 1.00 1.00
20060915 1759 B2914012 1.00 1.00 1.00
20060919 2350 B2825128 1.00 1.00 1.00
20060920 1800 B2825088 1.00 1.00 1.00
20060920 2346 B2815633 1.00 1.00 1.00
20060921 1728 B2834732 1.30 1.30 1.30
20060921 2330 B2825042 1.50 1.50 1.50
20060922 0527 B2825043 1.70 1.80 1.70
20060922 1128 B2825031 1.60 1.50 1.60
20060922 1729 B2834437 1.50 1.50 1.50
20060922 2330 B2825040 0.40 0.50 0.50
20060923 0529 B2834733 0.30 0.30 0.30
20060923 1128 B2825026 0.40 0.40 0.40
20060923 1729 B2825064 0.60 0.70 0.60
20060923 2330 B2825041 0.40 0.50 0.50
20060924 0529 B2825039 0.30 0.30 0.30
20060924 1729 B2825025 0.20 0.30 0.20
20060924 2329 B2825032 0.30 0.40 0.40
20060925 0529 B2824234 0.20 0.30 0.20 |