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Version 1.0.2
Created: March 13, 2003
Table of Contents- INTRODUCTION
- INSTRUMENT DESCRIPTION AND STATUS
- OVERVIEW
- DESCRIPTION OF INSTRUMENTS
- AIRS
- AIRS VIS/NIR
- AMSU-A 5
- HSB
- Relation of Fields of View of AIRS/AMSU/HSB
- AIRS SCIENCE PROCESSING SYSTEM
- SYSTEM OVERVIEW
- DATA PROCESSING VERSION 2.7
- LEVEL-1A PROCESSING
- LEVEL-1B PROCESSING
- V2.7 RELEASE OF L1B DATA INFORMATION
- DATA DISCLAIMER AND QUICK START QUALITY ASSURANCE
- Data Disclaimer
- Quick Start Quality Assurance
- AIRS
- AIRS IR channel characteristics
- Instrument state
- Radiometric calibration
- Spectral Calibration
- Spatial Calibration
- VIS/NIR
- Instrument state
- Radiometric calibration
- Pointing
- Enhanced L1B Product Since Sample Data Release
- VIS/NIR channel characteristics
- AMSU-A
- Instrument state
- Radiometric calibration
- Preliminary Pointing Analysis using Coastlines
- Relevant analysis
- AMSU-A channel characteristics
- HSB
- Instrument state
- Radiometric calibration
- Preliminary Pointing Analysis using Coastlines
- Relevant analysis
- HSB channel characteristics
- SAMPLE DATA READERS
- IDL Readers
The Atmospheric Infrared Sounder (AIRS) instrument suite is
designed to measure the Earths atmospheric water vapor and temperature
profiles on a global scale. It comprise a space-based hyperspectral
infrared instrument (AIRS) and two multichannel microwave instruments, the
Advanced Microwave Sounding Unit (AMSU) and the Humidity Sounder for Brazil
(HSB). The AIRS instrument suite is one of several instruments onboard the
Earth Observing System (EOS) Aqua spacecraft launched May 4, 2002.
Operational L1B Products of the AIRS/AMSU/HSB instrument suite on the EOS
Aqua spacecraft are now available for use by the general public. They can be
accessed on the web at the URL:
These data are in the standard HDF-EOS Swath format and can be used for
preliminary science evaluations. They include calibrated radiances for all
three instruments and Quality Assessment (QA) data. The radiances are well
calibrated; however, not all QA data have been validated. A product granule
contains 6 minutes of data. Thus there are 240 granules of each product
produced every day.
A complete description of the product file contents of the released L1B data
products can be found in the companion document titled AIRS Version 2.7
Released Files Description. A PDF file containing Version 1.1 of this
document, dated March 2003, is available at the link:
V2.7_Release_ProcFileDesc.pdf
The document provides for each L1B product:
- Dimensions for use in HDF-EOS swath fields (name, value, explanation)
- Geolocation fields (name, explanation)
- Attributes (name, type, extra dimensions, explanation)
- Along-track data fields (name, type, extra dimensions, explanation)
- Full swath data fields (name, type, extra dimensions, explanation)
- Special AIRS types for engineering data fields (name, type, explanation)
It also provides the product file naming and local granule identification
(LGID) conventions used in the identifier portion of the EOSDIS Core System
(ECS) and a table of all current Science, Engineering and Browse Products (L1A,
L1B and L2 Descriptions of the Level 1B data products provided in that document
and instrument and data features provided here are limited to the V2.7 released
data set. For additional information, please consult the AIRS public web site:
Additional information may be accessed at the following web sites:
The AIRS/AMSU/HSB instrument suite has been constructed to obtain
atmospheric temperature profiles to an accuracy of 1 K for every 1 km layer in
the troposphere and an accuracy of 1 K for every 4 km layer in the stratosphere
up to an altitude of 40 km. The temperature profile accuracy in the
troposphere will match that achieved by radiosondes launched from ground
stations. The advantage of the AIRS suite in orbit is the provision of rapid
global coverage. Radiosonde coverage of the Earths oceans is practically
nonexistent. In conjunction with the temperature profiles, the AIRS instrument
suite will obtain humidity profiles to an accuracy of 10% in 2 km layers from
the surface to the tropopause.
The Aqua Instrument Page provides guides to the instruments, including quicktime animations that illustrate their operation:
The AIRS infrared spectrometer acquires 2378 spectral
samples at resolutions, l/Dl, ranging from 1086 to 1570, in three bands: 3.74
m to 4.61 m, 6.20 m to 8.22 m, and 8.8 m to 15.4 m. A 360 degree
rotation of the scan mirror generates a cross-track scan line of IR data every
2.667 seconds. The spatial resolution at nadir is 13.5 km. This instrument
provides fine vertical scale resolution soundings of atmospheric temperature
and water vapor, and integrated column burden for trace gases.
The IR focal plane is cooled to 60 K by a Stirling/pulse tube cryocooler.
The scan mirror operates at approximately 265 K due to radiative coupling to
the Earth and space and to the 150 K IR spectrometer. Cooling of the IR optics
and detectors is necessary to achieve the required instrument sensitivity.
The Visible/Near-IR (VIS/NIR) photometer contains
four spectral bands, each with nine pixels along track, with a 0.185 degree
instantaneous field-of-view (FOV). It is boresighted to the IR spectrometer to
allow simultaneous measurements of the visible and infrared scene. The VIS/NIR
photometer uses optical filters to define four spectral bands in the 400 nm to
1000 nm region. The VIS/NIR detectors are not cooled and operate in the 293 K
to 300 K ambient temperature range of the instrument housing. The spatial
resolution at nadir is 2.3 km. The primary function of the AIRS VIS/NIR
channels is to provide diagnostic support to the infrared retrievals: setting
flags that warn of the presence of low-clouds or highly variable surface
features within the infrared field-of-view.
The AMSU-A
microwave multichannel radiometer consists of two physically separate units,
AMSU-A1 and AMSU-A2. Together they have 15 channels, measuring radiation in
the frequency span of 23 GHz to 90 GHz. Twelve channels (between 50 GHz and 60
GHz) are predominantly used for atmospheric temperature sounding. The
remaining three channels (24 GHz, 31 GHz and 89 GHz) are predominantly used for
atmospheric water vapor sounding. The rotating scanning mirror generates a
cross-track scan line every 8 seconds. The spatial resolution at nadir is 40.5
km.
The HSB microwave multichannel radiometer has 4 channels. One channel
measures radiation at 150 GHz and the other three are centered on 183.31 GHz.
All channels are used for atmospheric water vapor sounding. The rotating
scanning mirror generates a cross-track scan line every 2.667 seconds. The
spatial resolution at nadir is 13.5 km.
An AMSU-A FOV encompasses 9 AIRS FOVs (arranged in a 3x3 matrix) and 9 HSB
FOVs (arranged in a 3x3 matrix). Each AIRS FOV encompasses 72 Vis/NIR pixels
(arranged in a 9x8 rectangular array). This arrangement is illustrated in
Figure 1, which was produced from the geolocation information contained within
Granule 016 of data taken July 20, 2002. The large circle represents the 3.3
deg IFOV of an AMSU-A observation. The smaller colored circles represent the
1.1 deg IFOVs of the associated arrays of AIRS and HSB observations. The
colored rectangles represent the areas covered by the associated arrays of
VIS/NIR pixels.
Since granule 016 is a descending (nighttime) granule, the spacecraft track
tends toward the southwest. The scan direction as seen by an observer sitting
on the spacecraft and facing the direction of motion is left to right. Thus
the scan direction on the Earth for this granule is right to left in this
figure.
A granule of data contains 45 scansets, corresponding to 45 cross-track
scans of the AMSU-A mirror. The AMSU-A radiance data sampled in a scanset are
combined to create integrated radiances for 30 contiguous AMSU-A footprints.
Within each scanset are three scanlines, corresponding to 3 cross-track
scans of the AIRS and HSB mirrors. The AIRS and HSB radiance data sampled in
each scanline are combined to create integrated radiances for 90 AIRS and 90
HSB footprints.
The VIS/NIR instrument has an array of 9 detectors arranged along the
spacecraft track direction and look at the AIRS mirror. Sampling and
integration are arranged so that there are 8 cross-track VIS/NIR pixels
accumulated while the mirror sweeps through one AIRS instantaneous FOV.
Figure 1: AIRS/AMSU/HSB Footprint Pattern
The AIRS Science Processing System (SPS) is a collection of programs, or
Product Generation Executives (PGEs), used to process AIRS Science Data. These
PGEs process raw, low level AIRS Infrared (AIRS), AIRS Visible (VIS), AMSU, and
HSB instrument data to obtain temperature and humidity profiles.
AIRS PGEs can be grouped into three distinct processing phases for
processing: Level 1A, Level 1B and Level 2. Each consecutive processing phase
yields a higher-level data product. Levels 1A and 1B result in calibrated,
geolocated radiance products. Level 2 processing derives temperature and
humidity profiles. In addition to the standard processing PGEs, there are
additional Browse PGEs that are run to produce aggregate qualitative summary
for each standard product. Figure 2 is a diagram illustrating the processing
flow of the AIRS Science Processing System.
Figure 2: AIRS Science
Processing System Processing Flow |
Note, Level 2 products are not yet available. The Level 2 PGE will be included in a future release.
The V2.7 Release Science Processing Software (SPS) provided to the GSFC DAAC
for L1B Product Generation is version 2.7.12.0 and represents the best
refinement of all Level 1A and Level 1B PGEs as of January 21, 2003. It
contains working versions of all Level 1A and Level 1B software modules.
Specific features and characteristics of version 2.7.12.0 are described in
other sections of this documentation.
The enhancements to Level 1A and Level 1B reflect lessons learned from
analysis of post-launch data. The software is still under development, and JPL
plans to continue to upgrade PGEs and will deliver updated code modules to the
GSFC DAAC to support public release of Level 2 products during the middle of
2003 at approximately Launch + 13 months.
AIRS data processing begins with
receipt of Level 0 data from EDOS. When Level 0 data are received, Level 1A
PGEs are scheduled. The Level 1A PGEs perform basic house keeping tasks such
as ensuring that all the Level 0 data are present and ordering the data into
time of observation synchronization. Once the Level 0 data are organized,
algorithms perform geolocation refinement and conversion of raw Data
Numbers to Engineering Units (DN to EU). Finally, the level 1A data are
collected into granules of data (six minutes of instrument data) and are
forwarded to Level 1B PGEs for further processing.
Level 1B PGEs receive 240 granules of AIRS (AIRS IR, AIRS VIS, AMSU and HSB)
Level 1A EU data per day and produce calibrated, geolocated radiance products.
Calibration data and calibration control parameters are analyzed to develop
processing specifications for Level 1B processing. Then, the Level 1A data are
processed, yielding our Level 1B standard products. Each type of AIRS Level 1A
data is processed by a specialized Level 1B PGE. Each Level 1B PGE generates
240 granules of Level 1B standard products.
Level 1B PGEs produce 240 granules of 4 Level 1B standard products and 2
quality assessment (QA) subset products. Each granule is composed of 45
scansets. The Earth Science Data Type (ESDT) short names and normal granule
sizes are:
| Data Set | Short Name | Granule Size |
|---|
| L1B AMSU-A brightness temperatures | AIRABRAD | 0.4 MB |
| L1B HSB brightness temperatures | AIRHBRAD | 1.6 MB |
| L1B AIRS radiances | AIRIBRAD | 122.1 MB |
| L1B VIS radiances | AIRVBRAD | 21.0 MB |
| L1B AIRS QA | AIRIBQAP | 6.5 MB |
| L1B VIS QA | AIRVBQAP | 0.9 MB |
The AIRS Calibration Team documents the required inputs and outputs of the
AIRS IR and VIS/NIR Level 1B processing software, algorithms for converting
AIRS IR digital numbers to calibrated radiances, and QA algorithms and
indicators in Atmospheric Infrared Sounder (AIRS) Level 1B Visible,
Infrared and Telemetry Algorithms and Quality Assessment (QA) Processing
Requirements. Version 2.2 of this document, dated 2/14/03, is available
at the link:
L1B_req_v2.2.pdf
The interested user will find additional information on QA indicators for AIRS IR and VIS/NIR L1B products in this document.
Experience with on-orbit AIRS data prompted the AIRS Calibration Team to
alter some AIRS L1B algorithms (e.g. AutomaticQAFlag, DC Restore, pop
detection, Moon-in-view, offset, noise estimation and gain). A brief AIRS
Design File Memo describing these changes, dated 2/4/03, is available at the
link:
l1bqa_changes.pdf
An AIRS Design File Memo (ADF-579) provides the initial assessment of the on-orbit performance of the VIS/NIR system, dated 6/12/02. It is available at the link:
VisInitialCheckout_.pdf
Another AIRS Design File Memo (ADF-590-REVISED) dated 9/27/02 provides the
results of the first accurate determination of instrument gains of the VIS/NIR
detectors on-orbit via vicarious calibration in conjunction with the MISR-Terra
Calibration Team operations at Railroad Valley Playa, Nevada. It is available
at the link:
VisGainCalibration.pdf
The accompanying file:
Data_Disclaimer.pdf
provides information which affects the availability of data for ordering
(i.e., may be unavailable due to instrument outage or spacecraft maneuvering).
It also lists the known liens against each instrument.
The accompanying file:
QA_Quick_Start.pdf
Is a guide to the most basic quality assurance (QA) parameters that a novice user of AIRS/AMSU/HSB data should access to judge its quality.
The properties of the 2378 AIRS instrument detectors are individually listed
in self-documenting text files. Some properties of the channels change slowly
with time or discontinuously whenever the instrument is warmed by a spacecraft
safety shutdown or in a defrost cycle. Whenever this occurs, a recalibration
exercise is performed and a new channel properties file created. Thus a series
of these files will result. The L1B PGE must use the proper one for initial
processing and later on if the data must be reprocessed.
The file names contain a date, identifying the first date for which they are
valid (and supersede a channel properties file containing an earlier date). As
of this release, there are four such files covering the time period from
8/30/02 to the present. Text versions may be accessed through the following
links:
- Instrument is in nominal science mode (instrument
flag OpMode = Operate)
- The quality of the calibration is judged to be good
- Link
to paper, "First Radiometric Validation of AIRS on the EO using the 20
July 2002 Focus Day Data" by Aumann and Strow, which uses analysis of
(observed calculated) for data from a single, relatively cloud free granule
in the subtropical Atlantic ocean to confirm absolute radiometric accuracy of
better than 0.5 K. A representative portion of the bias spectrum from the
paper is shown in Figure 3.
Figure 3: Plot of
calculated radiometric residuals for clear-view ocean footprints. Units are
Kelvins. The plot is versus frequency in wavenumbers. |
- Link
to paper, "An Evaluation of the Accuracy of AIRS Radiances from Sea
Surface Temerature Measurements" by Hagan presents an analysis of
(buoy_obs_SST AIRS_TOA) for data from two months of nighttime AIRS
observations compared to buoy measurements co-located in space and time to
within 50km and 2 hours respectively. The global bias and standard deviation
are 0.1 1.1 K at 938 cm-1 and 0.3 1.1` K at 2616 cm-1.
- Radiometric sensitivity is excellent. Figure 4 is a display of the noise equivalent temperatures as a function of wavelength.
Figure 4: Plot of
channel Noise Equivalent Temperatures. Units are Kelvins. The plot is versus
wavelength in microns. |
- Preliminary validation indicates that the absolute spectral accuracy is
equivalent to less than 0.5% of the detector spectral response function (SRF)
full width at half maximum (FWHM). Spectral stability and sensitivity are
0.02% FWHM level. See Figure 5.
- The SRF centroids are provided in the
accompanying channel properties file.
Figure 5: Plot of calculated
spectral offsets. Units of focal plane displacement are
microns. |
AIRS data for June 14-18, 2002 have been
processed using a coastline detection to provide preliminary information on the
AIRS boresight. Please see the accompanying document,
AIRS_Boresight_Method.pdf for details.
Figures 6a and 6b show the results of this analysis for two processing
modes, scan and track direction processing. The two modes are consistent with
each other and consistent with a two kilometer offset in the beam position.
The satellite track direction is up and the mirror scan direction is left to
right in both figures. The figure axes are referenced to the WVS coastline map.
 |
 |
| Figure 6: Plot of calculated spatial residuals. Individual residuals are plotted in kilometers |
| (a): along-scan (i.e., cross-track) | (b): along-track |
The data come from a worldwide distribution of 43 granules that correspond
to clear areas of quality A through C as discussed in the above reference. We
carefully selected areas that had both large and small (but potentially useful)
regions of clear coastline in order to maximize the amount of data over the
short time period used in June. The data consist of 25 day and 18 night
scenes. The error bars on the graph denote the standard deviation of the
population. The standard deviation of the mean for these data would be about
6.6 times smaller (about 0.4 km) than the population standard deviation (about
2.8 km) if the distribution were gaussian, however, there are systematic errors
in the data, possibly from cloud contamination.
Optimal use of the AIRS data with AMSU and HSB data requires knowledge of
the AIRS boresight to about 2 km. Planned use of the AIRS visible for cloud
flagging requires that the boresight position be known to 1.3 km. These
requirements are both met with a standard deviation of the mean of about 2.2,
which is not unreasonable for these data. Users should be aware that there
appears to be a 2 km shift in the geolocation data in the +direction of the
mirror scan.
- Within each channel, detector-to-detector relative errors are believed to be ~1%. Absolute system calibration is good to ~10% in each channel.
- Geolocation has been validated to 0.16 degrees (corresponding to 2 km at nadir)
(Note: To reduce the data volume, not every VIS/NIR pixel is geolocated.
Instead, only the four corner pixels of the 9x8 grouping associated with each
IR footprint are geolocated. (A bi-linear interpolation can be used to locate
the remaining pixels.) In the data files, four-element arrays called
cornerlats and cornerlons carry this information. The first array element
is the upper-left pixel when viewing an image aligned with up being North.
The second element is the upper-right pixel. The third and fourth elements
refer to the lower-left and lower-right pixels, respectively.
- Release V2.7 of L1B data contains seven new Vis/NIR products over that
which were available in the July 20, 2002 Sample Data Release. These are
preliminary estimates of cloud and surface properties, and the Level 2 Support
files will contain more accurate values. The products are as follows (see the
accompanying interface specifications document for additional details):
- PrelimCldMapVis: At Vis/NIR resolution, a true/false flag for whether or not clouds are present in the pixel (1=cloudy, 0=clear, -1=unknown).
- PrelimClrPrcVis: At IR resolution, the percentage of the footprint believed to be clear.
- PrelimClrPrcVisErr: At IR resolution, an error estimate on the above quantity.
- PrelimCldPrcVis: At IR resolution, the percentage of the footprint believed to be cloudy.
- PrelimCldPrcVisErr: At IR resolution, an error estimate on the above quantity.
- PrelimNDVI: At Vis/NIR resolution, an estimate of the surface normalized
differential vegetation index (NDVI). This NDVI value is taken from a
global surface map made using AVHRR data from the early 1990s
prepared by the Global Land 1-km AVHRR Project. See the website <http://edcdaac.usgs.gov/1KM/1kmhomepage.html>.
- PrelimCldQA: A true/false flag for whether or not problems were encountered during cloud detection. A value of zero implies no problems detected, cloud and surface information believed to be reliable. A value of one implies results are suspect.
Figure 7: The approximate
spectral response of the four VIS/NIR channels. Three solid curves are
(l to r) Channels 1, 2, and 3. Dashed curve is Channel 4. |
Channel 1 (0.40 to 0.44 m) is designed to be most sensitive to aerosols.
Channels 2 (0.58 to 0.68 m) and 3 (0.71 to 0.92 m) approximate the response
of AVHRR channels 1 and 2, respectively, and are particularly useful for
surface studies. (AVHRR is an imaging instrument currently carried by NOAA
polar orbiting satellites.) Channel 4 has a broadband response (0.49 to 0.94
m) for energy balance studies.
AMSU-A
- Instrument is in nominal science mode
- Both AMSU
modules are in the optimal space view position
- The data have been
reprocessed with the current best calibration algorithm and calibration
parameters.
- Calibration accuracy is estimated to be on the order of 1 K
- Radiometric sensitivity is better than requirements see AMSU-A
channel characteristics table, below.
- The quality of the calibration is judged to be good, but at present
there are substantial scan biases. Modeling of the sidelobe pickup is under
way to correct these scan biases.
- Channel 7 has additional correlated noise, and should be avoided in
applications that use single measurements, such as comparisons with collocated
soundings. It may be used in applications in which some averaging is done
(i.e. gridding/binning or regional averages)
- Channel 6 exhibits additional correlated noise; similar to channel 7 but much smaller
- Channel 9 exhibits occasional popping, i.e. the calibration counts suddenly drop and then quickly recover. This typically occurs no more than once per orbit.
- Channel 14 may have correlated noise, but it is minor
- Valid for channels 1, 2, 3, 15 (window channels)
- Pitch error < 10% of FOV (< 4 km at nadir)
- Roll Error estimated to be less than 20% of FOV
- Yaw error estimated to be less than 30% of FOV at swath edge
- See Accompanying Document: MW_L1B_Assessment.pdf
which is based upon a status report given to the AIRS Science Team in September 2002 and has been updated as of March 10, 2003.
| Ch# | Module |
Center freq[MHz] | Stability[MHz] | Bandwidth[MHz] | On-OrbitNEdT[K] | T/VNEdT[K] | Pol |
|---|
| 1 | A2 | 23800 | 10 | 1x270 | 0.17 | 0.17 | V |
| 2 | A2 | 31400 | 10 | 1x180 | 0.19 | 0.25 | V |
| 3 | A1 | 50300 | 10 | 1x160 | 0.21 | 0.25 | V |
| 4 | A1 | 52800 | 5 | 1x380 | 0.12 | 0.14 | V |
| 5 | A1 | 53596115 | 5 | 2x170 | 0.16 | 0.19 | H |
| 6 | A1 | 54400 | 5 | 1x380 | 0.21 | 0.17 | H |
| 7 | A1 | 54940 | 5 | 1x380 | 0.21 | 0.14 | V |
| 8 | A1 | 55500 | 10 | 1x310 | 0.14 | 0.16 | H |
| 9 | A1 | [f0]=57290.344 | 0.5 | 1x310 | 0.14 | 0.16 | H |
| 10 | A1 | f0217 | 0.5 | 2x77 | 0.19 | 0.22 | H |
| 11 | A1 | f0322.448 | 1.2 | 4x35 | 0.22 | 0.24 | H |
| 12 | A1 | f0322.422 | 1.2 | 4x16 | 0.31 | 0.36 | H |
| 13 | A1 | f0322.410 | 0.5 | 4x8 | 0.43 | 0.50 | H |
| 14 | A1 | f0322.44.5 | 0.5 | 4x3 | 0.71 | 0.81 | H |
| 15 | A1 | 89000 | 130 | 1x2000 | 0.10 | 0.12 | V |
HSB
- Valid for channel 2 (window channel)
- Pitch error < 10% of FOV (< 1.5 km at nadir)
- Roll Error estimated to be less than 20% of FOV
- Yaw error estimated to be less than 30% of FOV at swath edge
| Ch# | Center freq[MHz] | Stability[MHz] | Bandwidth[MHz] | On-OrbitNEdT[K] | T/VNEdT[K] | Pol |
|---|
| 1 | AMSU-B channel 1 was not implemented for HSB |
| 2 | 150000 | 100 | 2x1000 | 0.58 | 0.68 | V |
| 3 | 1833101000 | 50 | 2x500 | 0.55 | 0.57 | V |
| 4 | 1833103000 | 70 | 2x1000 | 0.35 | 0.39 | V |
| 5 | 1833107000 | 70 | 2x2000 | 0.28 | 0.30 | V |
The AIRS Project releases to the broad scientific community sample data
readers under IDL to facilitate user community use of on-orbit Level-1B
The AIRS Project releases to the broad scientific community sample data
readers written in IDL to facilitate user community use of on-orbit Level-1B
AIRS/AMSU/HSB radiances.
an aid to give the user community a leg up in using the data. There is no
commitment to provide assistance to the broad user community beyond the release
of these readers.
read_swath_l1_airs.pro
minimal call sequence:
- read_swath_l1_airs, pattern, numfp, numline, tai, lat, lon, rad, solzen
input:
- pattern path/filename of AIRS L1B product to be read
output:
- numfp number of AIRS footprints in swath scanline
(usually = GeoXTrack = 90)
- numline number of AIRS scanlines in swath
(usually = GeoTrack = 135)
- tai array of AIRS footprint tai ( tai[numfp,numline] ), sec
- lat array of AIRS footprint latitudes ( lat[numfp, numline] ), deg
- lon array of AIRS footprint longitudes ( lon[numfp, numline] ), deg
- rad array of AIRS radiances ( rad[Channel, numfp, numline] ),
milliWatts/m**2/cm**-1/sterad where Channel = 2378
- solzen array of AIRS footprint solar zenith angles
( solzen[numfp,numline] ), deg
expanded call sequence:
- read_swath_l1_airs, pattern, numfp, numline, tai, lat, lon, rad, solzen
- full_swath_data_field_name_1=variable_1_to_hold_it
- full_swath_data_field_name_n=variable_n_to_hold_it
where the code supplied already supports these optional full swath data field names: scangang, sun_glint_distance, CalFlag, freq, topog, state
The user can add more optional data fields by using the code as an example.
read_swath_l1_vis.pro
minimal call sequence:
- read_swath_l1_vis, pattern, cornerlats, cornerlons, rad
input:
- pattern path/filename of VIS L1B product to be read
output:
- cornerlats array of VIS geodetic latitudes at the centers of the pixels at the corners of the IR footprint by channel in degrees north
- ( cornerlats[GeoTrack, GeoXTrack, GeoLocationsPerSpot,
Channel] ), deg
- cornerlons array of VIS geodetic longitudes at the centers of the pixels at the corners of the IR footprint by channel in degrees East
- (range from 180 to +180) ( cornerlons[GeoTrack, GeoXTrack, GeoLocationsPerSpot, Channel] ), deg
- rad array of VIS radiances
( rad[GeoTrack, GeoXTrack, Channel, SubTrack, SubXTrack] ),
- in Watts/m**2/micron/steradian
where Channel = 4, SubTrack = 9, SubXTrack = 8,
GeoTrack = 135, GeoXTrack = 90 and GeoLocationsPerSpot = 4.
- The storage order of the GeoLocationsPerSpot (corners) is:
- AlongTrack Foreward Edge, CrossTrack ScanStart Edge
- AlongTrack Foreward Edge, CrossTrack ScanEnd Edge
- AlongTrack Trailing Edge, CrossTrack ScanStart Edge
- AlongTrack Trailing Edge, CrossTrack ScanEnd Edge
- where foreward edge is the edge of the swath data field closest to the direction the satellite is traveling and scanend edge is the edge of the swath data field closest to the end of a crosstrack scan.
The example reader fills this array with the swath data field named radiances
The user can add more optional data fields by using the code as an example.
read_swath_l1_amsu.pro
minimal call sequence:
- read_swath_l1_amsu, pattern, numfp, numline, tai, lat, lon, rad, solzen
input:
- pattern path/filename of AMSU L1B product to be read
output:
- numfp number of AMSU footprints in swath scanline
(usually = GeoXTrack = 30)
- numline number of AMSU scanlines in swath
(usually = GeoTrack = 45)
- tai array of AMSU footprint tai ( tai[numfp,numline] ), sec
- lat array of AMSU footprint latitudes ( lat[numfp, numline] ), deg
- lon array of AMSU footprint longitudes ( lon[numfp, numline] ), deg
- rad array of AMSU radiances ( rad[Channel, numfp, numline] ), K
where Channel = 15. The example reader fills this array with
the swath data field named brightness_temp
- solzen array of AMSU footprint solar zenith angles
( solzen[numfp,numline] ), deg
expanded call sequence:
- read_swath_l1_amsu, pattern, numfp, numline, tai, lat, lon, rad, solzen
- full_swath_data_field_name_1=variable_1_to_hold_it
- full_swath_data_field_name_n=variable_n_to_hold_it
where the code supplied already supports these optional full swath data field names: scangang, sun_glint_distance, CalFlag, freq, topog, state
The user can add more optional data fields by using the code as an example.
read_swath_l1_hsb.pro
minimal call sequence:
read_swath_l1_hsb, pattern, numfp, numline, tai, lat, lon, rad, solzen
input:
- pattern path/filename of AMSU L1B product to be read
output:
- numfp number of HSB footprints in swath scanline
(usually = GeoXTrack = 90)
- numline number of HSB scanlines in swath
- (usually = GeoTrack = 135)
- tai array of HSB footprint tai ( tai[numfp,numline] ), sec
- lat array of HSB footprint latitudes ( lat[numfp, numline] ), deg
- lon array of HSB footprint longitudes ( lon[numfp, numline] ), deg
- rad array of HSB radiances ( rad[Channel, numfp, numline] ), K
where Channel = 5. The example reader fills this array with
the swath data field named brightness_temp
- solzen number of HSB scanlines in swath
- (usually = Geo array of HSB footprint solar zenith angles
( solzen[numfp,numline] ), deg
expanded call sequence:
- read_swath_l1_hsb, pattern, numfp, numline, tai, lat, lon, rad, solzen
- full_swath_data_field_name_1=variable_1_to_hold_it
- full_swath_data_field_name_n=variable_n_to_hold_it
where the code supplied already supports these optional full swath data field names: scangang, sun_glint_distance, satheight
The user can add more optional data fields by using the code as an example.
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Atmos Composition
