venus express radio science experiment vera · 2016. 4. 6. · venus conference 2016, oxford, uk....

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KVenus Express Radio Science VeRa

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Venus Express Radio Science Experiment VeRa

Bernd Häusler (1), Martin Pätzold (2)

and the VeRa Team

“Venus Express Legacy Session”

(1) Universität der Bundeswehr München,(2) Institute for Planetary Research, RIU

University Cologne

Oxford, UK, April 6, 2016

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List of Contents

• VeRa Team and Partners• VeRa – Science Topics - Mission• Instrument – Experimental Techniques• Achievements in Science

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The VeRa Team and Partners

• Universität der Bundeswehr, Germany (B. Häusler, T. Andert)• University Cologne, Germany (M. Pätzold, S. Tellmann)• University Bonn, Germany (M. Bird)• Stanford University (G. L. Tyler, R.A. Simpson, D. Hinson) • Royal Observatory Belgium, Brussels ( V. Dehant, P. Rosenblatt)• JAXA, Japan (T. Imamura)• NASA-JPL/DSN (S. Asmar, T. Thompson)• ESA – ESTEC/ ESOC/ ESAC (H. Svedhem, D. Titov, F. Jansen, S. Remus)

Funding

Financial support granted to teams of US, Belgium, Japan by their national space agencies. DLR funded partially travel costs for the German group.

Thanks to all who have supported VeRa !

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1Venus Express Radio Science VeRa

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VeRa – Science Topics

• Atmosphere• Ionosphere• Surface• Gravity Anomalies• Solar Corona

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VeRa-VEX Status Early in the Mission

• First occultation season 2006

• Begin of S-band anomaly (considerable drop in radiated power) ~ August 4, 2006 DOY216

VeRa experiments affected: SCO, OCC, BSR

• VEX thermal problems resulted in a revision of thermal rules, affecting also VeRa

• Consequence:

• No more BSR experiments (confirmation of the existence of a thinconductive layer at Maxwell Montes missing for the next decades)

• No more SCO experiments• Limitations in further OCC experiments (sun illumination, S/C body rates)

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6Note: Active Sun during Aug.- Nov. 2011 and during Febr.- March 2012

Solar Activity in the Venus Express Mission

Aerobraking

VEX mission

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Mission Operations SummaryData Analysis

CL receiver mode:

VeRa retrieved so far more than 800 profiles of

• Temperature• Neutral number density• Pressure• Electron Density

Occultation season # 16 (last radio science pass DOY 082, 23 March, 2014)

OL receiver mode:• Data analysis still in progress both at RIU/Cologne and JAXA .• Detection of very thin structures (< 1 km) in Venus mesosphere now possible.

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Mission Operations SummaryArchiving

• Level 2 data archived until 2014. • Selected temperature profiles available on request. • Complete level 4 data set available on Saturn Server @ RIU

by end of September 2016 (EURO Venus project)

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Instrument – Experimental Techniques

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VeRa Experiment Ultrastable Oscillator ( USO )

1.5 kg 5 WManufact. TIMETECH

133 10 −≈ ⋅Allan Deviation

Quartz USO connected toX/S-band transponder Serves as ultrastable reference frequency source

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11Note: X5.4 Flare occurred on orbit #2147 March 7, 2012

Oct. 9 2014 in orbit # ~ 3100

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Radio Science Measurement Techniques

Two frequencies are needed to separate dispersive effects (plasma ) from non-dispersive effects (orbit, neutral atmosphere )

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Receiving Techniques Used

Closed Loop Recording (CL): Groundstation receives a dynamically limited the carrier signal with a PLL and requires S/N: ~ 12dB

Open Loop Recording (OL): Groundstation samples incoming signal with 150 ksamples per second.Special digital processing techniques allow to recover a highly dynamic carrier signal out of noise. S/N: ~ 0 dBAmount of data for a typical occultation: ~ 4 GByte

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14next iteration step

Radio Science Occultation Technique:Principle: Ray Bending in Neutral Atmosphere

α(a)Abeltransformcalculation

• ΔF• geometry

Iterative calculation Refraction index “n(r)”

It is the bending angle which carries the information about the refraction indexα

Sensitivity: Δα ~10 -8 rad

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The Radio Occultation TechniqueConducting an Experiment

At Venus - in order to maximize receiving power - one has to dynamically steerthe radio beam in 3 axes through the atmosphere to compensate for the raybending effect (Bending angle < 7°, 3dB opening angle of antenna beam 1.7°)

Dedicated software (Matlab/Simulink based simulator) including amodel atmosphere was developed for this purpose by the Radio Science team.This allowed to calculate the HGA pointing angles expressed by quaternionsfor the 3-axis pointing maneuvers to guide the microwave ray throughthe atmosphere.

Pointing had also to obey the „thermal rules“.

First done by an experiment in an ESA mission. Flawless operations.

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Carrier Power in a Typical „Deep“ Occultation PassCL-Receiver

Both Channels Normalized in Power

0 500 1000 1500 2000 2500 3000 3500 4000 4500-180

-170

-160

-150

-140

-130

-120DoY228-2006 -DFT Power Spectral Density iter. step 1- s-band (cal. and dec.)

Pow

er d

ensi

ty [

dBm

/Hz]

time since [2006 8 16 1 22 5] [s] (UTC - ERT)

S-BandX-Band

Loss of carrier power in the atmosphere

due to defocusing and absorption

~ - 50 dB (X-band)!

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Atmospheric Frequency Shift of the VeRa X-Band - Carrier Signal During a Complete Occultation. CL vs. OL Technique.

VeRa was the first planetary Radio Science mission detecting the carrier signal throughout a complete occultation.

The carrier could be detected during times with the planetary disk occulting completely the satellite.

0 500 1000 1500 2000 2500 3000 3500 4000

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

x 104 Residual frequency - x-band - CL vs. OL - DoY204 - 2006

time since [2006 7 23 1 22 9] (samples - time resolution ~ 0.01s)

freq

uenc

y re

sidu

al [

Hz]

CL

OL

Loss of carrierl power in the atmosphere

due to defocusing and absorption

~ - 50 dB (X-band)!

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Achievements in Science

Characterized by an excellent cooperation within in the VEX Teamincluding the Akatsuki Team

Very competent support in the fields of mission/experiment planning and ground station operations

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Achievements in Science

VeRa turned out to be an extremely versatile instrument:Precise time and frequency measurements with microwaves allowed tocharacterize, determine, detect, discover:

•The ionospheric structure of Venus•Particles of meteoric origin in ionospheric plasma •Structure of Venus middle atmosphere•Zonal wind distribution of Venus middle atmosphere (VeRa, VIRTIS)•Cloud top structure (VeRa, VIRTIS)•Polar vortex•Planetary waves•Ubiquitous distribution of gravity waves in the atmosphere•Saturation of gravity wave power spectra (gravity wave breaking) •Thin-layered near neutral structure of Venus mesosphere•Thin inversion layer at tropopause (~ 1 km, ~ 10K)•H2SO4 g distribution in atmosphere•Dielectric properties of surface aereas and gravity properties•Solar corona effects

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Structure of the Venus IonosphereDiscovery of Meteor Layer

103 104 105 106

electron density (106 m-3)

100

125

150

175

200

225

250

275

300

altit

ude

(km

)

DOY204, 2006ingress

V2

V1

meteor layer

Pätzold et al., GRL, 2009

Ionopause

DiffusionRegion

Bulge

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Global Thermal Structure of Venus Middle AtmosphereLatitude vs. Pressure, Zonally Averaged

Tellmann et al., 2015

Anomalous thermal structure at high latitudesabove 70 km

„Cold Collar“~70 km

~ 60 km

~ 80 km

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Averaged Zonal Wind Velocity Based on Cyclostrophic Approximation. Derived from VeRa and VIRTIS Data

A. Piccialli et al., Icarus, 217, 2012

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Static Stability of Venus Middle Atmosphere as Observed by VeRa

Tellmann et al., JGR 2009

Convective regionwith

strong vertical gradients of velocity

Thin inversion layer~ 1 km

Gravity wave propagation

Wave breaking

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Discovery of Globally Distributed Gravity Waves in the Venus Atmosphere

Global distribution of the Potential Energy Ep of gravity waves (altitude range 65-80 km) detected by VeRa. Background: Topography measured by Magellan.

Tellmann et al., Icarus, 2012

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OL Processing of Multipath Effects Based on Wigner-Ville Transformation (see also Herrmann et al. Thursday presentation)

100 120 140 160 180

Refractivity

6107.5

6108.0

6108.5

6109.0

6109.5

6110.0

6110.5

6111.0

Rad

ius

[km

]

Open LoopClosed Loop

230 240 250 260 270 280

Temperature [K]

6105.0

6105.5

6106.0

6106.5

6107.0

6107.5

6108.0

6108.5

6109.0

6109.5

6110.0

6110.5

Rad

ius

Open LoopClosed Loop (with averaging)

1 km“ thick“ Inversion layer not detected every pass – but almost.

Mattei, Remus, 2010

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Discovery of Saturated Gravity Wave Spectraand Turbulence in the Upper Mesosphere

Power Spectral Density of vertical wave number spectra divided by N4 in the altitude interval 65-80 km and 75-90 km in selected latitude intervals . Shown also semi-empirical saturation curve (dotted).

Vertical diffusion coefficient :2.7-31 (m2s-1)

Ando et al., JAS, 72, 2015

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Convective layer

Vertical Resolution 70 m

Thin, near-neutral layers are frequently found above ∼60 km altitude in the high-resolution static stability profiles obtained by FSI in the middle and high latitude.

Indication for turbulence.Miyamoto et al., 2015

Static Stability Profiles Analyzed with the OL – FSI TechniqueSmall Scale Fluctuations – Thin Near Neutral Layers

FSI GO

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2206 2208 2210 2212 2214 2216 2218 2220 2222

00

00

200.0210.0220.0230.0240.0250.0260.0270.0280.0290.0

00

[K]Temperature at lat: -35°, local time: 3-4 h

~ 4 Day Variations at Constant Latitude and Local TimePresence of Planetary Wave

(possibly vert. propag. Rossby/Kelvin Wave)- see Presentation by Tellmann et al. (Thursday) -

Origin of large scale structure still not clear:Baroclinic instability? And/or possibly turbulent processes acting transfering small scale structures into large scale structures?

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Solar Induced Effects above Tropopause at 75° - 85° Lat.Presence of Wave # 2 Structure

Coldest temperatures located at the subsolar and antisolar points.

Tellmann et al., JGR, 2009

NoonEvening

Midnight

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H2SO4 g Absorption Effects Observed by VeRa- Presentation by J. Oshlisniok this Tuesday -

350 Profiles between 2006 and 2014J. Oschlisniok et al., 2016

Model is being developed supporting the picture of a meridional transport of H2SO4 g condensing into droplets in the upward branch and evaporating again in the downward branch of the Hadley cell assuming a significant polar depression.

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Latitude Dependence of the Cloud Top Altitude- Presentation by D. Titov this Tuesday -

Lee et al., Icarus, 2012

Background: VeRa temperature fieldCrosses: VIRTIS (near IR)Filled and open circles: Venera 15 (mid-IR)

Data suggest an increase of particle size in the upper cloud from equator to pole

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Simulation of Barotropic Instability in the Venus Atmosphere -Polar Vortex

- Presentation by H. Ando this Thursday -

Ando et al., 2016

Instability criteria metChange of sign of dq/dφ

Circumpolar temperaturedistribution

as simulated by AFES

Verical temperature structures from VeRa used qualitatively

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Baroclinic Structure of Venus Atmosphere in the Cloud Layer

----- potential temperaturepressure

Häusler, Andert, 2010

Piccialli, 2010

Instability criteria must be met.Unstable modes can develop in regions of low static stabillity with large gradients of zonal velocity creating planetary scale waves..

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Thank You For Your Attention

Venus Express Radio Science Experiment VeRa�List of ContentsThe VeRa Team and PartnersVeRa – Science Topics VeRa-VEX Status Early in the Mission� Mission Operations Summary�Data Analysis Mission Operations Summary�ArchivingInstrument – Experimental TechniquesVeRa Experiment �Ultrastable Oscillator ( USO )�Radio Science Measurement Techniques�Slide Number 13 Radio Science Occultation Technique:�Principle: Ray Bending in Neutral Atmosphere The Radio Occultation Technique�Conducting an Experiment �Carrier Power in a Typical „Deep“ Occultation Pass�CL-Receiver�Both Channels Normalized in PowerSlide Number 17Achievements in Science�Achievements in Science�Structure of the Venus Ionosphere�Discovery of Meteor LayerSlide Number 21Averaged Zonal Wind Velocity Based on Cyclostrophic Approximation. Derived from VeRa and VIRTIS DataSlide Number 23Slide Number 24OL Processing of Multipath Effects Based on Wigner-Ville Transformation (see also Herrmann et al. Thursday presentation) Discovery of Saturated Gravity Wave Spectra�and Turbulence in the Upper MesosphereSlide Number 27Slide Number 28Slide Number 29Slide Number 30Latitude Dependence of the Cloud Top Altitude�- Presentation by D. Titov this Tuesday -Simulation of Barotropic Instability in the Venus Atmosphere - Polar Vortex �- Presentation by H. Ando this Thursday -Slide Number 33 Thank You �For Your Attention

venus express radio science experiment vera · 2016. 4. 6. · venus conference 2016, oxford, uk....

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