SOFIE Mark Hervig, CEDAR Meeting, 20 June 2006 1 GATS The Solar Occultation for Ice Experiment SOFIE...

SOFIE

Mark Hervig, CEDAR Meeting, 20 June 20061

GATS

The Solar Occultation for Ice Experiment SOFIE

Mark Hervig, SOFIE Deputy PI

Larry Gordley, SOFIE PI

GATS Inc.

SOFIE


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Introduction

SOFIE was designed to measure PMCs and the environment in which they form

Measurement challenges:

PMCs occupy tenuous altitudes: 83 km / 0.006 mb

PMC particles: 50 nm radius / 80 cm-3 concentration

PMC signals are low

100 times lower than PSCs

1000 times lower than cirrus

Gas signals are 100 times lower than in the stratosphere

Solar Occultation can meet these challenges:

Brightest source

Relative measurements

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Solar Occultation

The sun rises and sets relative to the spacecraft (30 times a day).

SOFIE stares at the sun, measuring profiles of solar intensity during each rise & set

SOFIE signals yield atmospheric transmission, a relative measurement:

V

Vexo

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Measurement Objectives

Measurements in specific wavelength regions target specific gases or particles.

Measured transmission profiles are used to retrieve geophysical parameters:

Temperature

O3, H2O, CO2, CH4, and NO mixing ratios

PMC extinction

Vertical profiles from the tropopause to over 100 km, with 1.5 km resolution

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Measurement Geometry

SOFIE sample volume length = 280 km

SOFIE vertical resolution, Z = 1.5 km

ZT

RE

Excellent vertical resolution

Long horizontal path length

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Optical Layout

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Differential Absorption Measurements

Each SOFIE channel uses two detectors to make three measurements:

1. Strong band absorption

2. Weak band absorption

3. Difference signal, V = weak – strong

V reduces or eliminates common mode noise:

atmospheric interference, tracking jitter, chopper noise, sun spots

Simultaneous measurements of:

PMCs

Temperature

H2O

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Channel DescriptionChannel Band /

TargetCenter

Wavelength (m)

Difference Signal Gain

Detector

11 / O3 s 0.291

30 SiC, PV2 / O3 w 0.330

23 / PMC s 0.867

300 Ge, PV4 / PMC w 1.04

35 / H2O w 2.46

96 HgCdTe, PC6 / H2O s 2.62

47 / CO2 s 2.79

110 HgCdTe, PC8 / CO2 w 2.94

59 / PMC w 3.06

120 HgCdTe, PC10 / PMC s 3.12

611 / CH4 s 3.38

202 HgCdTe, PC12 / CH4 w 3.48

713 / CO2 s 4.32

110 HgCdTe, PC14 / CO2 w 4.65

815 / NO w 5.01

300 HgCdTe, PC16 / NO s 5.32

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Retrieved Parameters

Retrieval Precisionworst case estimates

Altitude Range(km)

PMC Interference

(signal fraction)

T 2.8 K 1 - 100 0%

O31 ppbv 15 - 100 50%

H2O 0.15 ppmv 15 - 100 0%

CO25.3 ppmv 15 - 100 0%

CH430 ppbv 15 - 95 90%

NO 2 107 cm-3 80 - 120 20%

PMCs V, 10-7

V, 10-9 km-1 cloud -

Vertical resolution: 1.5 km (over-sampled at 150 m)

Horizontal resolution: 280 km 4 km

SOFIE


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Geographic Coverage

AIM orbit is polar, noon - midnight crossings

SOFIE provides 30 occultations (soundings) per day

15 sunrises in the south, 15 sunsets in the north

Consecutive measurements are separated by 1.6 hours & 900 km

sunsets

sunrises

SOFIE coverage during one year

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Sun Sensor

Megapixel FPA, 701 nm wavelength

Pointing precision is 0.5 arcsec

Measurements of solar extent provide refraction angle

Refraction angles are used to retrieve temperature profiles

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PMC Measurements

Retrievals of particle extinction (optical cross section / volume = km-1)

10 wavelengths from 0.33 - 5 m

•Radiometer signals (10 's)

= 0.330, 0.867, 1.04, 2.46, 2.94, 3.06, 3.12, 3.48, 4.65, and 5.01 m

Digitization limit = 1.1 10-7 (km-1)

•Difference signals (2 's)

Ch 2: = 0.95 m, gain = 300, digitization limit = 4 10-10 (km-1)

Ch 5: = 3.09 m, gain = 120, digitization limit = 9 10-10 (km-1)

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Integral PMC Properties

The infrared PMC signal is due to absorption which is directly proportional to r3 and therefore particle volume density, Vice,

Vice = C () (1))

Where C is a constant, () is extinction in km-1, and Vice is in m3 cm-3.

Constants for Equation 1.

(m) C

2.94 964.9

3.06 369.1

3.19 838.8

4.63 17758.3

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PMC Size Distribution Retrievals

PMC measurements spanning 0.3 to 5 microns are key will allow retrievals of complete PMC size distributions.

Retrieval considerations:

Particle shape:

Spherical (Mie)

Non-spherical (T-matrix)

Size distribution form:

Lognormal

Gaussian

Discrete (# bins = # 's)

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Cosmic Dust / Smoke

•Cosmic dust measurements are sparse and incomplete

•Current understanding based on scant observations combined with theory

e.g., Hunten et al. [1980], Kalashnikiva et al. [2000]; Rapp et al. [2002]

PMC volume densities are about 0.08 m3 cm3

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Smoke Signals in SOFIE Data

Predictions based on CARMA smoke model [Rapp et al., 2002]

SOFIE channel #2 (0.86 & 1.03 m)

Radiometer signals are below the digitization limit.

V signal of 90 counts at peak, but 30% of this is due to molecular scattering

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Correlative Measurements

AIM is seeking correlative measurements: Validation and enhanced science

Altitude: Focus on mesosphere, but SOFIE observes trop - 100 km

Latitude: 65 - 85 north & south

Time: focus on polar summer, desire other times

Measurements: PMC, PMSE, dust, aerosols, T, O3, H2O, CO2, CH4, NO

The AIM website (aim.hamptonu.edu) will provide

Measurement locations

Coincidence alerts (automated)

Coincidence criteria will vary depending on the geophysical parameter

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Summary

Continuous coverage of 65 - 85 latitude, north & south

Measures profiles of:

Temperature

O3, H2O, CO2, CH4, and NO mixing ratios

PMC extinction

SOFIE online: sofiedata.org

AIM online: aim.hamptonu.edu

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Backup slides follow

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Sun Sensor

Two basic components:Fast steering mirror1024 x 1024 focal plane array (FPA)

701 (11) nm wavelength

7.14 arcsec pixel dimension, 18 arcsec FOV (FWHM)

S/C is solar-pointing during SOFIE occultation

SOFIE pointing should only manage S/C jitter

Testing indicates 0.5 arcsec precision

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System Technical Resources

RESOURCE POST CDR CBE MEASUREDMATURE

ALLOTMENT

Mass36.7 kg

(minus bus cabling fixtures)38.0 kg 42.2 kg

Envelope Controlled by MICD

Average Power67.7 W

[50.5 W Electronics Unit, 17.2 W Instrument Unit]

52 W[38.8 W Electronics Unit, 13.2 W Instrument Unit]

85.2 W

Peak Power 107.6 W 85 W

Pin-puller Peak Power

32.2 W for < 0.5 sec, [130 mW Pre and Post Fire]

28 W during < 0.5 sec Fire

Survival Heater Average Power

15.2 W

Survival Heater Peak Power

62.8 W 59 W

Daily Data Volume 168 Mbits/day 168 Mbits/day 200 Mbits/day

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Commissioning Phase

WEEK 1

1. APPLY SURVIVAL HEATER POWER 2. APPLY SYSTEM POWER3. EXERCISE BASIC COMM

*APERTURE COVER NOT RELEASED

WEEKS 2-3

1. EXERCISE FULL COMM AND SYSTEM FUNCTIONALITY

*APERTURE COVER NOT RELEASED

WEEKS 4-5

1. RELEASE APERTURE COVER 2. PERFORM INITIAL SCIENCE AND CALIBRATION CHECKOUTS 3. VERIFY POINTING AND STABILIZATION CONTROL

1 MONTH COMMISSIONING

PHASE

SOFIE commissioning will use SDL & GATS personnel

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Channel Separation Module

Detector Opticsand Detector

OpticalElement #

CollimatedInput Beam

2.577 -2.632

2.427 -2.475

2.907-2.967

2.740 -2.793

3.472 -3.546

3.333 -3.401

3.160 -3.226

3.030 -3.091

4.255 -4.444

4.951 -5.051

4.630 -4.740

5.263 -5.376

0.286 -0.294

0.323 -0.333

0.848 -0.877

1.010 -1.053

Dichroic B S: Reflect UV, NIR;Transmit IR

Dichroic B S: Reflect <2.967Transmit > 3.030

Dichroic B S: Reflect .286-.333;Reflect .848-1.053 & 4.255-5.376: Transmit 2.427-3.546

Metal Mirror

Channel SeparationModule Filter Layoutas ordered April 2004

6 5

8 7

17

18B12

10

9

13

1514

16

11

19

4

2

3

1

Detector at 208K

Detector at 233K

Detector at 260K

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SOFIE Overview

Vertical resolution: 1.5 km, over-sampled at 150 m

Horizontal resolution: 280 km 4 km

16 bit digitization

Retrievals:

Temperature / Pressure

O3, H2O, CO2, CH4, NO

PMCs (10 wavelengths from 0.330 to 5.01 m)

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Implications of MAGIC Dust Measurements

•Mesospheric Aerosols Genesis Interaction and Composition (MAGIC)

Rocket-borne particle collector using a carbon impact grid

Lab analysis reveals particle size, concentration, and composition

•MAGIC flight over Wallops indicates cumulative smoke concentrations of 106 cm-3

Cumulative over radii from 1 - 3 nm and altitude from 76.7 - 93.5

•CARMA model (Markus Rapp) gives cumulative concentrations of 2.2 104 cm-3

MAGIC concentrations are 46 times greater than CARMA model

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SOFIE Signals Considering MAGIC Concentrations

CARMA smoke concentrations were scaled by 46 at all sizes and altitudes

SOFIE channel #2 (0.86 & 1.03 m)

radiometer signal is 30 times higher than digitization limit

V signal of 2800 counts at peak

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System Calibration Overview

System Functionality Requirement Result

Nonlinearity < 0.5% < 0.5% calibration uncertainty on all bands

RSR – Out of Band Energy Desired < 1% < 0.5% on all bands

Thermal Stability < 6400 Counts < 30 Counts

Pointing Ability < 15 arcsec < 2 arcsec (elev)

Pointing Knowledge < 1 arcsec < 0.4 arcsec (elev)

Signal to Noise Measured margin > 1 (except NO channel, 0.9)

Science Time Stamp Accuracy

< 2.5 ms < 100 us

SOFIE Mark Hervig, CEDAR Meeting, 20 June 2006 1 GATS The Solar Occultation for Ice Experiment SOFIE...

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