Title: The Solar Occultation for Ice Experiment SOFIE
1The Solar Occultation for Ice Experiment SOFIE
- Mark Hervig, SOFIE Deputy PI
- Larry Gordley, SOFIE PI
- GATS Inc.
2Introduction
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
3Solar 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
4Measurement 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
5Measurement Geometry
SOFIE sample volume length 280 km
Excellent vertical resolution Long horizontal
path length
ZT
RE
SOFIE vertical resolution, ?Z 1.5 km
6Optical Layout
7Differential Absorption Measurements
- Each SOFIE channel uses two detectors to make
three measurements - Strong band absorption
- Weak band absorption
- 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
8Channel Description
9Retrieved Parameters
- Vertical resolution 1.5 km (over-sampled at 150
m) - Horizontal resolution 280 km ? 4 km
10Geographic 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
11Sun 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
12PMC 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)
13Integral 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.
14PMC 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 Gauss
ian Discrete ( bins ?'s)
15Cosmic 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
16Smoke 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
17Correlative 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) Coincide
nce criteria will vary depending on the
geophysical parameter
18Summary
- 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
19Backup slides follow
20Sun 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
21System Technical Resources
22Commissioning Phase
SOFIE commissioning will use SDL GATS personnel
23Channel Separation Module
24SOFIE 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)
25Implications 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
26SOFIE 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
27System Calibration Overview