# Presentation: 202939

## Slide 1

## Occultation Science from the Sixties to Present

- T. P. Yunck and W. G. Melbourne
- Jet Propulsion Laboratory
- California Institute of Technology
- OPAC-1
- Graz, Austria
- 16-20 September 2002

## Origins-I:  Optical Occultation

- Stellar Occultation by Venus

## Slide 4

## Venus passing behind the Moon

## Moon-Saturn Occultation

- November 2001

## Moon-Saturn Occultation

- Entry

- November 2001

## Moon-Saturn Occultation

- Exit

- November 2001

## ‘Pseudo’ Optical Occultation 

- ‘Pseudo’ Optical Occultation
- of Jupiter Rings

## Grazing Stellar Occultation at Jupiter

## Pluto Stellar Occultation

- July 20, 2002

- The only planet not yet visited by a spacecraft

## Images of Pluto and Charon

- Constructed from Occultation Measurements

## Mariner IV at Mars

- Mariner IV at **Mars**
- July 1965

- Origins-II:  Planetary
- Radio Occultation

## Mariner IV Occultation at Mars: Two Competing Proposals

*Amazing facts:*  At 10 cm wavelength, 1 free electron will cancel the refractive effect of 2.5 x 1011 CO2 molecules.

## Mars

- Mariner IV
**Mars**
- 15 July 1965
- ( JPL wirephoto )

## Mariner IV Occultation at Mars:  Earliest Results

## Mariner IV Occultation at Mars:  Refined Results

## Mariner V at Venus

- 19 October 1967

## Mariner V Occultation at Venus: Separate Stanford & JPL Experiments

- Amplitude and phase based retrievals

## Mariner V Occultation at Venus: Temperature Profile Comparison

- Fjeldbo et al., 1971

## Pioneer Venus Orbiter

- 1979-1982

- First recovery of zonal winds from pressure contours

- Data taken over multiple seasons

## Outer Planets – I Jupiter and Saturn

- Outer Planets – I Jupiter and Saturn

## Outer Planets: 

- Outer Planets:
- Occultation Retrieval Challenges

- Uncertain composition and mixing
- 	Uncertain rotation rates
- 		Pronounced oblateness

## Saturn’s Strange Moon 

- Saturn’s Strange Moon
- Voyager Occultation of Titan

- Surface pressure was unknown to within a factor of ~1000   (answer:  ~1.5 bars)

- High altitude methane clouds

## Saturn Ring Occultation 

- Saturn Ring Occultation

- The rings act as a vast, thin, complex diffraction screen.

- Sampling of the phase-amplitude hologram allows detailed recon-struction of the ring structure

## Saturn Ring Occultation

- Marouf, Tyler, Rosen, 1986

- This ‘inverse Fresnel filtering’ improves resolu-tion by x50-90 over the ~15 km Fresnel limit

## Outer Planets – II Uranus and Neptune

- Outer Planets – II Uranus and Neptune

## Uranian Rings...

- Voyager Stellar
- Occultation

- Voyager Radio
- Occultation

## Neptunian Rings...

## Occultation Subjects: A Group Portrait

## An Observation on the Terrestrial Planets

- This atmosphere is too thin

- This atmosphere is too thick

## Just

- right...

## What took so long...?

- Need a lot of transmitters and a lot of LEO receivers
- GPS did not fit the paradigm:
- – One-way only
- – Need flight USOs?
- – Dithered GPS signal
- – Need classified receiver?
- – Suppressed GPS carrier
- – Crude pseudorange only?
- – Multipath a major concern
- – Need high-gain antennas?

## Earth Occultation – Early Concepts

- Fishbach, 1965:  Stellar occultation from LEO

- Lusignan et al., 1969:  Radio sounding with tandem LEO’s at a fixed separation

- Gurvich and Krasil’nikova, 1987:  Navigation satellites for sensing Earth atmosphere

## GPS Geoscience Instrument

- EOS-A, EOS-B and Space Station
- (1988-1992)

- Three Antennas
- 18 Channels
- Full Sky View

**POD**
**Geodesy**
**Ionosphere Mapping**
**Atmospheric Occultation**

## The GPS-MET Experiment 

- The GPS-MET Experiment
- on MicroLab-I
- 1995 - ?

## CHAMP

- SAC-C

- GRACE

## Coming Attractions...

- COSMIC/Rocsat3 (6)

- EQUARS
- C/NOFS
- NPOESS (3)
- METOP
- ACE+ (4)
- TerraSAR-X ?