The Solar Occultation for Ice Experiment
SOFIE
Mark Hervig, SOFIE Deputy PI
Larry Gordley, SOFIE PI
GATS Inc.
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
1
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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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

SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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Measurement Geometry
SOFIE sample volume length = 280 km
Excellent vertical resolution
ZT
Long horizontal path length
RE
SOFIE vertical resolution, Z = 1.5 km
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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Optical Layout
SOFIE
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Mark Hervig, CEDAR Meeting, 20 June 2006
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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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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Channel Description
Channel
1
2
3
4
5
6
7
8
Band /
Target
Center
Wavelength
(m)
1 / O3 s
0.291
2 / O3 w
0.330
3 / PMC s
0.867
4 / PMC w
1.04
5 / H2O w
2.46
6 / H2O s
2.62
7 / CO2 s
2.79
8 / CO2 w
2.94
9 / PMC w
3.06
10 / PMC s
3.12
11 / CH4 s
3.38
12 / CH4 w
3.48
13 / CO2 s
4.32
14 / CO2 w
4.65
15 / NO w
5.01
16 / NO s
5.32
Difference
Signal Gain
Detector
30
SiC, PV
300
Ge, PV
96
HgCdTe, PC
110
HgCdTe, PC
120
HgCdTe, PC
202
HgCdTe, PC
110
HgCdTe, PC
300
HgCdTe, PC
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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Retrieved Parameters
Vertical resolution: 1.5 km (over-sampled at 150 m)
Horizontal resolution: 280 km  4 km
Retrieval
Precision
worst case estimates
Altitude Range
(km)
PMC
Interference
(signal fraction)
T
2.8 K
1 - 100
0%
O3
1 ppbv
15 - 100
50%
H2O
0.15 ppmv
15 - 100
0%
CO2
5.3 ppmv
15 - 100
0%
CH4
30 ppbv
15 - 95
90%
NO
2  107 cm-3
80 - 120
20%
PMCs
V, 10-7
V, 10-9 km-1
cloud
-
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
sunrises
SOFIE coverage
during one year
sunsets
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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)
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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)
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
AIM
online:
sofiedata.org
online: aim.hamptonu.edu
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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Backup slides follow
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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Sun Sensor
Two basic components:
Fast steering mirror
1024 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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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System Technical Resources
RESOURCE
POST CDR CBE
MEASURED
MATURE
ALLOTMENT
Mass
36.7 kg
(minus bus cabling fixtures)
38.0 kg
42.2 kg
Envelope
Controlled by MICD
Average Power
67.7 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
Survival Heater
Average Power
32.2 W for < 0.5 sec,
[130 mW Pre and Post Fire]
28 W during < 0.5 sec Fire
15.2 W
Survival Heater
Peak Power
62.8 W
59 W
Daily Data Volume
168 Mbits/day
168 Mbits/day
200 Mbits/day
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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Commissioning Phase
SOFIE commissioning will use SDL & GATS personnel
WEEK 1
1. APPLY SURVIVAL HEATER POWER
2. APPLY SYSTEM POWER
3. EXERCISE BASIC COMM
*APERTURE COVER NOT RELEASED
1 MONTH
COMMISSIONING
PHASE
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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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Channel Separation Module
5
6
Channel Separation
Module Filter Layout
as ordered April 2004
2.427 2.475
2.577 2.632
7
8
2.740 2.793
2.9072.967
12
18B
Metal Mirror
0.848 0.877
1.010 1.053
4
Dichroic B S: Reflect <2.967
Transmit > 3.030
11
0.286 0.294
0.323 0.333
1
10
3.333 3.401
3
2
3.472 3.546
3.160 3.226
9
3.030 3.091
13
17
Dichroic B S: Reflect .286-.333;
Reflect .848-1.053 & 4.2555.376: Transmit 2.427-3.546
Dichroic B S: Reflect UV, NIR;
Transmit IR
19
14
4.630 4.740
Collimated
Input Beam
4.255 4.444
15
4.951 5.051
Detector at 208K
16
Optical
Element #
Detector at 233K
Detector Optics
and Detector
Detector at 260K
5.263 5.376
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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)
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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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
Science Time Stamp
Accuracy
Measured margin > 1 (except NO channel, 0.9)
< 2.5 ms
< 100 us
SOFIE
GATS
Mark Hervig, CEDAR Meeting, 20 June 2006
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