CloudSat Project
A NASA Earth System Science Pathfinder Mission
Level 1A Auxiliary Data Process
Description and Interface Control
Document
Version: 00.00
Date: June 15, 2001
Prepared by:
________________________________________
Dale Reinke, CIRA Software Engineer
Cooperative Institute for Research in the Atmosphere
Colorado State University
Fort Collins, CO 80523
Approvals
Date
Deborah Vane
Deputy Project Scientist
Date
Graeme Stephens
Project Scientist
Date
Donald Reinke
Data Processing Center Lead Engineer
Date
Steve Durden
CPR System Engineer
Date
Li Li
CPR Level 1B Processing Engineer
Questions concerning the document and proposed changes shall be addressed to
Dale Reinke
970-491-8928
reinkedg@cira.colostate.edu
2
Contents
Contents .............................................................................................................................. 3
1. Introduction ............................................................................................................. 4
1.1.
Overview ............................................................................................................. 4
2. Inputs....................................................................................................................... 5
2.1.
CloudSat Level 0 CPR Science Data .................................................................. 5
2.2.
CRC..................................................................................................................... 5
2.3.
Definitive Ephemeris .......................................................................................... 6
2.4.
VTCW Correlation.............................................................................................. 6
2.5.
Digital Elevation ................................................................................................. 6
2.6.
Surface Characteristics........................................................................................ 7
3.
Process .................................................................................................................... 9
4. Outputs .................................................................................................................. 10
4.1.
CloudSat Level 1 A Auxiliary Data .................................................................. 10
3
1. Introduction
1.1.
Overview
The Level 1A Auxiliary Data (1A-AUX) will be created to provide additional parameters
as input into the Level 1B CPR data generator. Each 1A-AUX file will directly
correspond to a Level 0 CPR Science data file. These two files will be then used to
create the Level 1B CPR data products.
4
2. Inputs
The input data files into the 1A-AUX generator are as follows:
2.1.
CloudSat Level 0 CPR Science Data
The CPR digital system will average the received power at each range bin and will
collect various engineering and housekeeping data. These data will be written to the
spacecraft recorders and downlinked. The data is formatted as 0.16 s blocks of radar
data, each preceded by a header. This format is defined in the Digital Subsystem HighLevel Design Document. A block with header would have the following format (as
implemented in C):
struct {
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
unsigned
} hdr0;
char
char
char
char
char
char
char
char
char
char
char
char
char
char
char
char
char
char
char
/* structure for CPR data block */
block_start_ID[4];
sec[2]; /* seconds since last VTCW update from spacecraft */
time_code[5];
/* VTCW time code */
msec[2];
/* millisec since last one second pulse */
pri;
/* pulse repetition interval (1/PRF) */
cal;
/* calibration source (nd, load, or antenna) */
data_window_delay; /* tx pulse to rx window (1.6 us units) */
echos_in_flight;
pulses_transmitted[2]; /* no. of pulses in the .16 s block */
mode;
pulse_width;
/* width of xmit pulse (3.1 – 3.8 us) */
grid;
/* grid enable setup */
pll_lock;
/* phase-locked loop lock status */
telemetry[40];
envelope[16];
motor[4];
echo[NECHO];
/* summed recv'd signals, first is cal_data */
frame[2];
/* frame counter */
crc[2];
/* cyclic redundancy code */
A file of Level 0 data available for processing would have some number of data blocks,
where each block would have a format like that just presented. The Level 0 CPR data
should be nearly identical to the raw data stream output from the radar with duplicate
packets removed from the raw data to create Level 0. The cyclic redundancy code (CRC)
in each block, or frame, is used to determine whether there were bit errors in the
downlink for that particular frame.
This data will be transferred to CIRA via FTP approximately 8 times per day.
2.2.
CRC
The CRC file will contain information about when a bad CRC was identified.
5
This data will be transferred to CIRA via FTP approximately 8 times per day.
2.3.
Definitive Ephemeris
A definitive ephemeris is an ASCII text file that contains position and velocity vector
information corresponding to a particular UTC time and orbit number. A sample file
follows:
Ephemeris Report
Signature:
Extracted:
Title:
Subtitle:
Ephemeris:
Spacecraft:
Equinox:
Attitude:
2000/347
2000/347
2000/347
2000/347
2000/347
2000/347
2000/347
2000/347
2000/347
2000/347
2000/347
2000/347
2000/347
2000/347
OASYS v2.4.6i (97 Jun 05), Integral Systems, Inc.
12/13/00 21:40:20
/msn/db/xxxx/OPS/oasys/bxxxx348.eph
[xxxx] xxxx
MEME of Epoch [2451545.000000 days]
3-Axis Stblzd
UTC
Orbit Number
orbits
ECI Pos.x
km
ECI Pos.y
km
ECI Pos.z
km
ECI Vel.x
m/sec
ECI Vel.y
m/sec
ECI Vel.z
m/sec
00000.000
00001.000
00002.000
00003.000
00004.000
00005.000
00006.000
00007.000
00008.000
00009.000
00010.000
00011.000
00012.000
00013.000
2179.0872
2179.0874
2179.0876
2179.0878
2179.0879
2179.0881
2179.0883
2179.0885
2179.0886
2179.0888
2179.0890
2179.0892
2179.0893
2179.0895
2220.0433
2219.7121
2219.3782
2219.0417
2218.7025
2218.3606
2218.0160
2217.6688
2217.3189
2216.9663
2216.6111
2216.2532
2215.8926
2215.5293
5511.5507
5507.5205
5503.4836
5499.4402
5495.3900
5491.3333
5487.2700
5483.2000
5479.1235
5475.0403
5470.9505
5466.8542
5462.7512
5458.6417
3537.2949
3543.7321
3550.1650
3556.5936
3563.0179
3569.4380
3575.8537
3582.2650
3588.6721
3595.0748
3601.4732
3607.8672
3614.2569
3620.6422
-329.84931
-332.52421
-335.19871
-337.87281
-340.54652
-343.21982
-345.89272
-348.56521
-351.23728
-353.90894
-356.58018
-359.25100
-361.92140
-364.59136
-4026.8911
-4033.5298
-4040.1636
-4046.7927
-4053.4168
-4060.0361
-4066.6506
-4073.2601
-4079.8648
-4086.4645
-4093.0594
-4099.6493
-4106.2343
-4112.8144
6439.3294
6435.0515
6430.7658
6426.4723
6422.1710
6417.8620
6413.5452
6409.2207
6404.8884
6400.5483
6396.2005
6391.8450
6387.4817
6383.1107
This data will be transferred to CIRA via FTP once a day.
2.4.
VTCW Correlation
A VTCW Correlation file correlates VTCW time to UTC every 16 seconds.
This data will be transferred to CIRA via FTP once a day.
2.5.
Digital Elevation
The Digital Elevation file matches latitude and longitude values with the elevation at that
point . This is a static database that resides at CIRA.
Data Description:
GTOPO30 is a global digital elevation model (DEM) resulting from a collaborative effort
led by the staff at the U.S. Geological Survey's EROS Data Center in Sioux Falls, South
Dakota. Elevations in GTOPO30 are regularly spaced at 30-arc seconds (approximately
1 kilometer). The current release represents the completion of global coverage of 30-arc
second elevation data that have been available from the EROS Data Center beginning in
6
1993. Several areas have been updated and the entire global data set has been
repackaged, so these data supersede the previously released continental data sets.
GTOPO30 covers the full extent of latitude from 90 degrees south to 90 degrees north,
and the full extent of longitude from 180 degrees west to 180 degrees east. The
horizontal grid spacing is 30-arc seconds (0.008333333333333 degrees), resulting in a
DEM having dimensions of 21,600 rows and 43,200 columns. The horizontal coordinate
system is decimal degrees of latitude and longitude referenced to WGS84. The vertical
units represent elevation in meters above mean sea level. The elevation values range from
-407 to 8,752 meters. In the DEM, ocean areas have been masked as "no data" and have
been assigned a value of -9999. Lowland coastal areas have an elevation of at least 1
meter, so in the event that a user reassigns the ocean value from -9999 to 0 the land
boundary portrayal will be maintained. Due to the nature of the raster structure of the
DEM, small islands in the ocean less than approximately 1 square kilometer will not be
represented.
2.6.
Surface Characteristics
The Surface Characteristics file matches latitude and longitude values with the type of
terrain at that point (i.e. land, sea, ice, coast).
This is a static database that resides at CIRA.
Background
The U.S. Geological Survey's (USGS) Earth Resources Observation System (EROS)
Data Center, the University of Nebraska-Lincoln (UNL) and the Joint Research Centre of
the European Commission have generated a 1-km resolution global land cover
characteristics data base for use in a wide range of environmental research and modeling
applications (Loveland and others, 2000). The land cover characterization effort is part of
the National Aeronautics and Space Administration (NASA) Earth Observing System
Pathfinder Program and the International Geosphere-Biosphere Programme-Data and
Information System focus 1 activity. Funding for the project is provided by the USGS,
NASA, U.S. Environmental Protection Agency, National Oceanic and Atmospheric
Administration, U.S. Forest Service, and the United Nations Environment Programme.
The data set is derived from 1-km Advanced Very High Resolution Radiometer
(AVHRR) data spanning a 12-month period (April 1992-March 1993) and is based on a
flexible data base structure and seasonal land cover regions concepts. Seasonal land cover
regions provide a framework for presenting the temporal and spatial patterns of
vegetation in the database. The regions are composed of relatively homogeneous land
cover associations (for example, similar floristic and physiognomic characteristics) which
exhibit distinctive phenology (that is, onset, peak, and seasonal duration of greenness),
and have common levels of primary production.
7
Rather than being based on precisely defined mapping units in a predefined land cover
classification scheme, the seasonal land cover regions serve as summary units for both
descriptive and quantitative attributes. The attributes may be considered as spreadsheets
of region characteristics and permit updating, calculating, or transforming the entries into
new parameters or classes. This provides the flexibility for using the land cover
characteristics data base in a variety of models without extensive modification of model
inputs.
The analytical strategy for global land cover characterization has evolved from methods
initially tested during the development of a prototype 1-km land cover characteristics data
base for the conterminous United States (Loveland and others, 1991, 1995; Brown and
others, 1993). In the U.S. study, multitemporal AVHRR data, combined with other
ancillary data sets, were used to produce a prototype land cover characteristics data base.
The land cover characteristics data base is available for each of five continental areas and
for the entire globe. The continental land cover characteristics data is provided in the
Interrupted Goode Homolosine Equal Area projection (see Steinwand, 1994, and
Steinwand and others, 1995, for a complete description of this projections).
Interrupted Goode Homolosine Projection Parameters
The data dimensions of the Interrupted Goode Homolosine projection for the global land
cover characteristics data set are 17,347 lines (rows) and 40,031 samples (columns)
resulting in a data set size of approximately 695 megabytes for 8-bit (byte) images. The
following is a summary of the map projection parameters used for the Interrupted Goode
Homolosine projection:
Projection Type: Interrupted Goode Homolosine
Units of measure: meters
Pixel Size: 1000 meters
Radius of sphere: 6370997 m.
XY corner coordinates (center of pixel) in projection units (meters):
Lower left: (-20015000, -8673000)
Upper left: (-20015000, 8673000)
Upper right: (20015000, 8673000)
Lower right: (20015000, -8673000)
8
3. Process
Examine 1A-AUX Data
Processing Directory
No
Is there data?
No
Yes
Do we have a
corresponding definitive
emphemeris?
Yes
Open Level 0 CPR
Science Data file and create
corresponding 1A-AUX file
Read next record from
Level 0 file
Yes
Retrieve data for the
corresponding 1A-AUX
record from the other input
files. Compute the latitude,
longitude, and altitude for the
corresponding 1A-AUX
record.
Write the corresponding
1A-AUX record
More Level
0 records?
No
Close Level 0 and 1A-AUX
files.
Remove Level 0 file and
move 1A-AUX file to transfer
directory.
9
4. Outputs
4.1.
CloudSat Level 1 A Auxiliary Data
Each block of 1A-AUX data would have the following format:
NAME
Frame Number
Data Status Flags
FORMAT
DESCRIPTION
2-byte
Sequential Frame Number
integer
1 byte total Various status fields as
as follows: detailed below:
1 bit
1 bit
1 bit
1 bit
1 bit
1 bit
1 bit
1 bit
Missing frame
Land
Sea
Ice
Coast
CRC flag
Navigation status
Clock overflow flag
VALUES
1 - 65535
0=false or 1=true
0=false or 1=true
0=false or 1=true
0=false or 1=true
0=false or 1=true
0=false or 1=true
0=false or 1=true
0=false or 1=true
10 bytes as Frame UTC time converted
follows:
from VTCW time as below:
UTC Time
2-byte integer
1-byte integer
1-byte integer
1-byte integer
1-byte integer
1-byte integer
1-byte integer
2-byte integer
Fractional Orbit
4-byte float
Number
Spacecraft
4-byte float
Geodetic Latitude
Spacecraft
4-byte float
Geodetic Longitude
Spacecraft
Geodetic Altitude
DEM Elevation
Year (4-digits)
Month
Day of Month
Hour
Minute
Second
Millisecond
Day of Year
Orbit number and fractional
part of an orbit
The geodetic latitude of the
spacecraft
The geodetic longitude of
the spacecraft
The altitude of spacecraft
4-byte float above the Earth Ellipsoid
(km)
2-byte
Surface elevation at
integer
geodetic lat/lon (m)
0 – 9999
1 – 12
1 – 31
0 – 23
0 – 59
0 – 59
0 – 999
1 – 366
TBD
-90.0 – 90.0
-180.0 – 180.0
TBD
0 – 8850
10