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 4October 9-10, 2006

MM5 AnalysisCONT02 (Oct 15-31, 2002)

Wettzell WVR Workshop 5October 9-10, 2006

Hart x-sect

Wettzell WVR Workshop 6October 9-10, 2006

Hart plan view

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?

Wettzell WVR Workshop 12October 9-10, 2006

Wettzell WVR Workshop 13October 9-10, 2006

D4: 3 km grid2-way nesting

5º 10º

D1: 81 km grid2-way nesting

5º 10º

5º 10º 5º 10º

D2: 27 km grid2-way nesting

D3: 9 km grid2-way nesting