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Atmospheric Corrections Study
Virgilio B. Mendes, FC/UL
Erricos C. Pavlis, JCET/UMBC
Atmospheric Corrections Study
• During the October 2002 ILRS Workshopwe presented results from the NMFs forvarious wavelengths.
• It was discussed and agreed at that time tolook into improved zenith delaycomputations and to undertake acomparison study using the 1999 - 2002period of LAGEOS 1 & 2 ILRS NPs.
E. C. Pavlis
Atmospheric Corrections Study
• Four years of LAGEOS 1 & 2 ILRS NPs
• Reduced with identical modeling in weekly arcs,using NASA Goddard’s GEODYN II (3 iterations)
• One set of reductions used the 1973 Marini-Murrayatmospheric delay model (MM )
• A second set used a modified Saastamoinen zenithdelay model with the Mendes et al. mapping functionFCULb (NMF )
• Compared the Dry, Wet and Total delay differences
E. C. Pavlis
Atmospheric Corrections Study
• Used the refractive index computation of P.Ciddor (1996):
• With group refractive index for dry air:
• And group refractive index for water vapor:
E. C. Pavlis
Atmospheric Corrections Study
• Define zenith delay as:
• After some derivations we get the hydrostaticterm:
• And the non-hydrostatic term:
E. C. Pavlis
Atmospheric Corrections Study
• A modified version of the subroutines wedistributed last year, FCULa and FCULb, wasdeveloped based on the new derivation.
• In addition to the improved zenith delay model,the new subroutines were implemented in a testversion of GEODYN II in a way that the dry andwet components are computed and reportedseparately in the corrections file.
• The results reported here were obtained using thenew version of the model and s/w.
E. C. Pavlis
-4
-2
0
2
4
6
0 50000 100000 150000 200000 250000 300000 350000
∆∆∆∆ Tro
p_(M
M-N
MF
PC
) [m
m]
Obs. No.
E. C. Pavlis / GSFC
Atmospheric Corrections Study
LAGEOS 1
0
2000
4000
6000
8000
10000
12000
14000
16000
-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
L1 MM NMFPC 2002 d t
∆Trop_(MM-NMFPC)
Cou
nt
Range
LAGEOS 11999 - 2002
∆∆∆∆Trop_(MM-NMFPC)LAGEOS 1-3.17Minimum5.00Maximum
306215Points0.41Mean0.71Median0.89RMS0.79Std Deviation
E. C. Pavlis / GSFC
Atmospheric Corrections Study
-4.00
-2.00
0.00
2.00
4.00
6.00
.001 .01 .1 1 5 1 0 2 0 3 0 5 0 7 0 8 0 9 0 9 5 9 9 99.9 99.9999.999
LAGEOS 1
∆∆∆∆ Tro
p_(M
M-N
MF
PC
)
Percent
E. C. Pavlis / GSFC
Atmospheric Corrections Study
-5
0
5
0 50000 100000 150000 200000 250000 300000 350000
∆∆∆∆ Tro
p_(M
M-N
MF
PC
) [m
m]
Obs. No.
E. C. Pavlis / GSFC
Atmospheric Corrections Study
LAGEOS 2
0
10000
20000
30000
40000
50000
60000
70000
80000
-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
L2 MM+NMFPC 1999-02 cor dat
∆Trop_(MM-NMFPC)
Cou
nt
Range
LAGEOS 21999 - 2002
˘Trop_(MM-NMFPC)LAGEOS 2
304637Points
0.37Mean
0.50Median
0.80RMS
0.71Std Deviation
E. C. Pavlis / GSFC
Atmospheric Corrections Study
-5
0
5
.001 .01 .1 1 5 1 0 2 0 3 0 5 0 7 0 8 0 9 0 9 5 9 9 99.9 99.9999.999
LAGEOS 2∆∆∆∆ Tro
posp
heric
Del
ay (
Mar
ini M
urra
y -
NM
FP
C)
[mm
]
PercentE. C. Pavlis / GSFC
Atmospheric Corrections Study
Atmospheric Corrections StudySummary
• We used four years of high quality SLR ILRS NPobservations on LAGEOS 1 & 2: 1999 - 2002
• Reduced then in identical fashion except for theatmospheric delay models, M-M and NMF+PCand modified Saastamoinen ZD
• Dry component exhibits ~1 mm bias• Wet component shows an order of magnitude
smaller bias• Overall, the residual differences are smaller by
~0.8 mm with NMF yielding the smaller residuals
E. C. Pavlis
Atmospheric Corrections StudyFuture Work
• The current study used the standard release ILRS NPs
• To validate the new model and discriminate between thatand the M-M, we need data with higher sensitivity
• There are several months of low elevation FR data taken atGrasse, and NP data from Graz.
• A new analysis (underway) incorporates these data sets
• We are still testing the new models for wavelengthsensitivity and developing the mechanism to adapt themfor multi-wavelength SLR (although it seems that thewavelength dependence is rather small)
E. C. Pavlis
