# Presentation: 935761

## Remote Radio Sounding Science For JIMO

**J. L. Green, B. W. Reinisch, P. Song, S. F. Fung, R. F. Benson, **
**W. W. L. Taylor, J. F. Cooper, L. Garcia, D. Gallagher, and T. Markus**

**Jupiter Icy Moons Orbiter Community Science Workshop**
**June 13, 2003, LPI Houston, TX**

## Sounding Overview from IMAGE

**Two successive Radio Plasma Imager (RPI) plasmagrams**
- Virtual range vs frequency
**RPI simultaneously probes the plasmasphere and field-aligned paths in the local hemisphere**
**RPI measurements can be used to investigate N****e**** distributions through echo inversion techniques**

**Reinisch et al., 2001**
**Carpenter et al., 2002**

## Goal 3: Radiation Environment

**Radio sounding provides vertical ionospheric electron density (N****e****) profiles**
**Field-aligned echoes provide N****e**** profiles along magnetic field lines **
- Ganymede - indication of closed or open field lines and magnetospheric extent
** ****Resonance and passive observations provide accurate determination of *****in situ***** measurements of N****e**** and magnetic field strength**
** ****Passive observations of Jovian radio emissions (1 kHz to 40 MHz) provides provides an index to magnetosphere state or activity level**
**Dynamics and variability of Jovian magnetosphere-moon interactions can be studied on various time scales**

## Ionospheres of Icy Moons: Existing Observations

**• ****In addition, Ganymede has a magnetosphere**

## Possible Ionospheric Profiles

**Vertical N****e**** profiles (in orbit plane) images aids in production analysis**

## Future Observations with Sounding

## Jovian Emission Background

**Precise *****In situ***** plasma densities from array of resonances**

**Kurth et al., 1997**

## In Situ Plasma Measurements

**Two near apogee passes of IMAGE/RPI on successive quiet and disturbed days**
**Can determine the accuracy of:**
**f****p**** to ~ 1%**
**f****g**** to ~ 0.1%**
**March 30, 2001 - top panel**
- Clear nfg resonances (n=2-14)
- fg kHz
- No fp resonance implies fp < 6 kHz
**March 31, 2001 - bottom panel**
- Increase of **B** with nfg only to     n = 6
- Resonances also at D1, D1, D2+, fp, fuhr, Q3 and Q4

**Benson et al., 2002**

**fD1-**

**fD1**

## Goal #1 &2: Potential for Life/Origins

**Radio sounding at frequencies above the peak ionospheric f****p ****will reach and penetrate moon surface**
- Low frequency subsurface penetrating radar (LF-SPR)
**Can determine thicknesses of various layers to a certain depth**
- Provides information on ice, impurities, water layers, and vertical temperature profile
- Lower frequencies penetrate deeper
- Ionosphere measurements will be necessary to correct subsurface penetrating radar measurements

## Earth Example: Ground Echoes

**Ionosphere measurements will be necessary to correct ground penetrating radar measurements**

## Summary Assessment for JIMO

**A radio sounding instrument provides significant capability**
- Ionospheric & magnetospheric sounding
- Subsurface sounding
*In situ* resonance measurements
- Passive plasma wave measurements
**Supports 3 major JIMO mission goals**
**Complements other JIMO instruments (ie: VHF radars)**
**Very low developmental risk: Proven instruments**
**High power needed for:**
- Remote sensing at greater distances/depths
- Higher data rates
**Provides a high science value for the JIMO mission**

## Backup Material

## Principles of Radio Sounding

**Radio waves are reflected at wave cutoffs (n = 0)**
**In a cold, magnetized plasma**
- Ordinary (O-mode): Wave frequency =  *f**p*
- Extraordinary (X-mode): Wave frequency =
**Echoes from reflections perpendicular to density contours (direct) or at cutoffs along field lines**

**Echo**

**Refracted rays**

**Refracted rays**

- n=0

- n>0

- n<0

## Types of Sounding Echoes

## Overview of Radio Plasma Imager (RPI)

**RPI transmits coded EM waves and receives resulting echoes at 3 kHz to 3 MHz**
- Uses advanced digital processing techniques (pulse compression & spectral integration)
**RPI uses a tri-axial orthogonal antenna system**
- 500 meter tip-to-tip X and Y axis dipole antennas
- 20 meters tip-to-tip Z axis dipole antenna
- X axis antennas are used for all transmissions
- Echo reception is accomplished on all three
**Basic RPI measurements of an echo at a selected frequency **
- Amplitude
- Time delay (distance or range from target)
- Direction of arrival
- Wave polarization (ordinary or extra-ordinary)
- Doppler shift and frequency dispersion
***In situ***** density and resonances measurements**

## IMAGE Orbit

## Earth’s Ionospheric Measurements

**Ionograms are echo amplitudes plotted as a function of apparent range versus frequency**
- Note: Apparent range plotted as decreasing values
**Two wave polarizations are found (extraordinary - X and ordinary - O)**
**Observations contain: direct echoes, resonances, and ground reflections**
**Standard inversion technique used to determine the vertical N****e**** profile **

## IMAGE/RPI Field-Aligned Echoes

## Variations in Orbital Configuration

**Study ionospheric production processes over orbital time scales**
**Measure dynamics and temporal variability of Jovian magnetosphere-moon interactions **

## Plasmagram with Echoes and Resonances

**What does RPI see?**
**Clear X mode echo and cutoff frequency identified**
- fx =
**Clear resonances at: **
- nfg (n = 1-3)
- fqn (n = 2, 3)
**Determine f****p****/f****g**** = 0.99 in a self consistent manner**

**Reinisch et al., 2001**

## Field-Aligned Profile Inversion

**N****e**** is obtained from an inversion technique **
**Two traces are used to obtain N****e**** in both hemispheres **

**IMAGE **
**Location**

## Continued Refilling of the Plasmasphere

**Measured**

**Quiet Day Model**

## Passive Plasma Wave Measurements

**Passive observations provides a measure of “activity” in the Jovian magnetosphere (solar wind and non-solar wind influences) **

**Carr et al., 1983**