High Altitude Equatorial Clouds as Seen with the OSIRIS InfraRed Imager A.E. Bourassa, D.A....
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Transcript of High Altitude Equatorial Clouds as Seen with the OSIRIS InfraRed Imager A.E. Bourassa, D.A....
High Altitude Equatorial Clouds as Seen with the OSIRIS InfraRed Imager
A.E. Bourassa, D.A. Degenstein, N.D. Lloyd and E.J. Llewellyn
Institute of Space and Atmospheric StudiesDepartment of Physics and Engineering Physics
University of Saskatchewan
Outline
1) The instrument, the geometry and the technique
2) Some detections
3) Some statistics
4) To be done
Channel 1: 40 nm passband at 1530 nm
Channel 2: 10 nm passband at 1273 nm
Channel 3: 10 nm passband at 1263 nm
Each channel has 128 pixels, approximately 20 covered with mask
The IRI Instrument
LinearPhotodetectorArray
Optic AxisPixel
f
Field of View
LinearPhotodetectorArray
Optic AxisPixel
f
Field of View
SOLID EARTH
The Geometry To Scale
one image is collected every 2 seconds for approximately 2800 images per orbit
the orbit is approximately circular at 600 km above the equator
dusk-dawn orbit
in general only one hemisphere is lit
different illumination conditions for ascending and descending nodes
18 km cross section18 km cross section
Missing data from scan mode
Typical Data Collection
the scan or spacecraft nod results in missing IRI data
note the bright enhancements at the lower tangent altitudes
data for March, 2002
18 km cross section18 km cross section
Missing data from scan mode
Cloud detectionCloud detection
clouds clearly stand out against daytime nighttime trends
An Orbit of Limb Profiles
The Typical Profile
when the sun is up
this profile is measured most of the time at mid to high latitudes
it is even measured frequently at low latitudes
this profile is frequently measured near
the equator
The Typical and the not so Typical Profiles
layer at 18 km
when the sun is up
this profile is measured most of the time at mid to high latitudes
it is even measured frequently at low latitudes
note that the equatorial region is only fully illuminated on the ascending track of the satellite.
80
85
90
95
100
-90 -45 0 45 90Latitude
SZ
A
Ascending
Descending
80
85
90
95
100
-90 -45 0 45 90Latitude
SZ
A
Ascending
Descending
this allows for the characterization of an unperturbed signal
note that even for the lower sun on the descending node the equatorial enhancement is still there
Solar Conditions for March, 2002
0
2
4
6
8
10
78 82 87 91 95Solar Zenith Angle
Bri
ghtn
ess
(AU
)
Unperturbed Conditions for March, 2002
the ascending and descending nodes are plotted as a function of Solar Zenith Angle
the criteria used for cloud detection
any scatter above a threshold level is considered a cloud
this is done with the vertical profiles and is evaluated as a function of altitude
Detected Clouds for March, 2002
detections for a single day in March, 2002
contoured map of cloud detection for a three week period in spring, 2002
the clouds are between 17 and 20 km
all latitudes are sampled with approximately the same frequency.
Total Counts for April, 2002
Detected Clouds for January, 2002
Detected Clouds for February, 2002
Detected Clouds for March, 2002
Detected Clouds for April, 2002
Detected Clouds for May, 2002
More Detected Clouds
More Detected Clouds
More Detected Clouds
More Detected Clouds
More Detected Clouds
More Detected Clouds
More Detected Clouds
More Detected Clouds
A Different Look At the Data
The previous pictures just counted occurrences
The next set will look at percentages of occurrences
These pictures need more work as single hit outliers can really make a mess with the contouring routines that are used
Percentage of Hits in Early 2002
Percentage of Hits in Early February
Percentage of Hits in Late April Early May
To Be Done
1) Determine the best statistic to use
2) Process all data and map geographic, seasonal and time of day
3) Do more correlations with visual channels
4) Attempt to retrieve optical depths