Resolving Sub-Fresnel-Scale Atmospheric Structure and Diffracting Limbs in Planetary Radio Occultation

Details Resolving Sub-Fresnel-Scale Atmospheric Structure and Diffracting Limbs in Planetary Radio Occultation Resolving Sub-Fresnel-Scale Atmospheric Structure and Diffracting Limbs in Planetary Radio Occultation

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p52a0569h&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #P52A-0569

Physics

Optics

5409 Atmospheres: Structure And Dynamics, 6900 Radio Science, 6964 Radio Wave Propagation

Scientific paper

indent=0.25in The resolution of atmospheric profiles retrieved from radio occultation is often limited by diffractive blurring. Based on the laws of geometrical optics, the Abel inversion used to generate atmospheric profiles cannot typically resolve sub-Fresnel-scale structure nor compensate for diffraction from planetary limbs. In this research, these diffractive effects have been investigated in forward simulations of radio occultation. To achieve better vertical resolution, a multiple phase screen (MPS) approach has been implemented to manipulate the angular spectrum of forward-simulated data, effectively reducing the Fresnel zone size [Karayel, E. T. and D. P. Hinson, Sub-Fresnel-scale vertical resolution in atmospheric profiles from radio occultation, Radio Sci., 32(2), 411-423, 1997]. Consequently, small atmospheric structure can be more accurately reconstructed than by using Abel inversion alone. In simulation, this technique was able to resolve a smooth, 40 m refractivity perturbation of magnitude 10-7 superposed over the refractivity profile for a Mars-like atmosphere. The simulated atmosphere had a refractivity of ~4\times 10-6 and a scale height of approximately 9 km. The Fresnel scale in this simulation was approximately 250 m. Using a variation of the same MPS technique, models for diffraction from planetary limbs have been explored in order to better understand the limb diffraction seen in occultation data from satellites (e.g., Mars Global Surveyor) as well as its effect in atmospheric profile retrieval. Such occultation data contain clear indications of diffraction from the planetary limb, having oscillations with spatial frequencies corresponding to the Fresnel scale. Consequently, this investigation attempts to model limb diffraction as the result of single and multiple, non-parallel knife-edges and incorporate it into the method for profile retrieval.

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