wettzell wvr workshop1 october 9-10, 2006 use of nwm forecasts for converting t b to delay arthur...
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Wettzell WVR Workshop 1October 9-10, 2006
Use of NWM forecasts forconverting TB to delay
Arthur NiellMIT Haystack Observatory
Mark LeidnerAER, Inc.
Wettzell WVR Workshop 2October 9-10, 2006
Questions
Can a high resolution Numerical Weather Model forecast improve the calculation of delay from WVR brightness temperature?
Can the use of NWM and WVR improve the atmosphere estimation in geodetic VLBI and GPS?
Wettzell WVR Workshop 3October 9-10, 2006
Mesoscale NWP Model
PSU/NCAR 5th generation nested grid mesoscale model (MM5)
Horizontal spacings 81, 27, 9, and 3 km Pressure level output from surface to 10
hPa (30 levels) Initialized with NCEP global model 12 hour forecasts initialized every 6 hours
Wettzell WVR Workshop 7October 9-10, 2006
Model - 1
NT
WT
time
elevation
frequency of WVR measurement
( , , ) true brightness temperature
( , , ) brightness temperature from NWM
error in
( , , ) brightness temperature from WVR
error
B
N
N
W
t
f
T t f
T t f
T
T t f
N
WT
in
( , , ) delay calculated from NWM
error in
( , , ) delay to be calculated for WVR
error in
W
N
N
W
W
T
t f
t f
Wettzell WVR Workshop 8October 9-10, 2006
Model - 2
( ,90 )( , )
( ,90 , )
N iN i j
N i j
tr t f
T t f
•Define ratio of delay to brightness temperature from NWM
•If this ratio from MWM is accurate, then WVR delay is related to the true TB by:
( ,90 ) ( , ) ( ,90 , )W i N i j B i jt r t f T t f
Wettzell WVR Workshop 9October 9-10, 2006
Model - 3•WVR TB is related to true TB by offset and scale factor
( ,90 , ) ( ,90 , )W i j W W B i jT t f a b T t f
• Then the delay corresponding to the brightness temperature measured by the WVR will be:
( ,90 ) ( , ) ( ( ,90 , ))W i N i j W i jt r t f a b T t f
( ,90 ) ( , ) ( ( ,90 , ))W i N i j W i jt r t f a b T t f ( ,90 ) ( , ) ( ( ,90 , ))W i N i j W i jt r t f a b T t f
• and the model for the wet delay in the geodetic analysis will be:
( , ) ( , ) [ ( , ) ( ( ,90 , ))]W i w i N i j W i jt m t r t f a b T t f
• Thus in geodetic analysis estimate (in principal) only two parameters, a and b, instead of 72 ZWDs (every 20 min).
Wettzell WVR Workshop 10October 9-10, 2006
Questions - 1
What is the error in rn?
Are a and b constant over 24 hours? There is information in all frequencies.
How can other frequencies be included? e.g. use Onsala X parameter (kge)?
What horizontal resolution is needed for this to be useful?
Wettzell WVR Workshop 11October 9-10, 2006
Questions - 2
VLBI data will be reanalyzed many times as models improve. Is it practical to do analysis instead of forecast at 3 km resolution? Will the rn improve?