MULTIWAVELENGTH REFRACTION MODELING IMPROVEMENTS FOR SLR OBSERVATIONS
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G. Hulley, E. C. Pavlis, V. B. Mendes and D. E. Pavlis, MULTIWAVELENGTH REFRACTION MODELING IMPROVEMENTS FOR SLR OBSERVATIONS, https://cddis.nasa.gov/lw14/docs/papers/atm6_epm.pdf
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This is a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
Atmospheric refraction is an important accuracy-limiting factor in the use of satellite laser ranging (SLR) for high-accuracy science applications. In most of these applications, and particularly for the establishment and monitoring of the TRF, of great interest is the stability of its scale and its implied height system. The modeling of atmospheric refraction in the analysis of SLR data comprises the determination of the delay in the zenith direction and subsequent projection to a given elevation angle, using a mapping function. Standard data analyses practices use the 1973 Marini-Murray model for both zenith delay determination and mapping.
This model was tailored for a particular wavelength and is not suitable for all the wavelengths used in modern SLR systems. Improved refraction modeling is essential in reducing errors in SLR measurements that study variations in the Earth's gravity field and crustal motion (especially for the vertical component), as well as monitoring sea-level rise, post-glacial rebound and other geophysical phenomena. Current models of atmospheric delay only take into account the elevation angle of the transmitted ray and assume a spherically symmetric atmosphere. In order to improve models of atmospheric delay, azimuthal asymmetries
(gradients) in the atmospheric refractive index still need to be modeled and researched. In the past, VLBI and GPS groups used NCEP fields to estimate gradients in the atmosphere and to improve their analysis products. We are now entering a new era where global snapshots can be available from satellite-borne instruments on a daily basis. We will be using atmospheric
profiles from an instrument aboard the AQUA satellite called the Atmospheric InfraRed Sounder (AIRS) in order to compute the gradients in the North-South and East-West directions as well as the atmospheric delay resulting from these gradients. Comparisons will be made between the delay calculated using a direct AIRS ray-tracing method, and the best available model [Mendes and Pavlis, 2004]. A new method to calculate the delay, called Two-Color laser ranging will be compared to the Marini-Murray model with data taken from the Matera SLR station in 2003.