TITLE:  POES NOAA AVHRR HRPT Data [NCAR/EOL]


CONTACTS:

Steve Williams
NCAR/EOL
P.O. Box 3000
Boulder, CO 80307-3000

phone: 303-497-8164
email: sfw@ucar.edu


1.0  DATA SET OVERVIEW


This data set contains 1-km resolution 5-channel AVHRR (Advanced Very High 
Resolution Radiometer) HRPT (High Resolution Picture Transmission) data from the
NOAA POES satellites (K/L/M/N).  These data were retrieved from the NOAA
CLASS archive.  The data are in Level 1-b format and cover the T-REX period
(1 March to 30 April 2006).  They cover the region from 34-40 N and 115-126 W.


2.0  INSTRUMENT DESCRIPTION


Complete information on the NOAA POES AVHRR instumentation is available from
the NOAA KLM User's Guide:

http://www2.ncdc.noaa.gov/docs/klm/

The Advanced Very High Resolution Radiometer (AVHRR) sensor is carried on NOAA's 
Polar-orbiting Operational Environmental Satellites (POES) starting with TIROS-N 
in 1978. Onboard the TIROS-N, NOAA-6, 8 and 10 POES Satellites, the AVHRR Sensor
measures in four spectral bands, while on the NOAA-7, 9, 11, 12 and 14 POES 
Satellites, the sensor measures in five bands. The AVHRR/3 sensor on NOAA-15 
and 16 measures in six bands though only five are transmitted to the ground at any time.

The visible data values may be converted into albedos and the IR data into 
radiances or temperatures using the calibration information which is appended but 
not applied. Latitudes and longitudes of 51 benchmark data points along each scan 
are included. Other parameters appended are: time codes, quality indicators, solar 
zenith angles, and telemetry.

The AVHRR provides a global (pole-to-pole) on-board collection of data from all 
spectral channels. At an 833 km altitude, the 110.8 degree scan equates to a swath 
27.2 degrees in width (at the Equator), or 2,600 km, centered on the subsatellite 
track. This swath width is greater than the 25.3 degree separation between 
successive orbital tracks, providing overlapping coverage (side-lap).

For LAC and HRPT, the instantaneous field-of-view (IFOV) of each channel is 
approximately 1.4 milliradians (mr) leading to a resolution at the satellite 
subpoint of 1.1 km for a nominal altitude of 833 km. Since GAC data contain only 
one out of three original AVHRR lines and the data volume and resolution are 
further reduced by averaging every four adjacent samples and skipping the fifth 
sample along the scan line, the effective resolution is 1.1 x 4 km with a 3 km gap 
between pixels across the scan line. This is generally referred to as 4 km resolution.


3.0  DATA COLLECTION AND PROCESSING


NCAR/EOL conducted no processing or quality control on these data.


NOAA Polar-orbiting Operational Environmental Satellites obtain global imagery 
daily. These data are transmitted to the Command and Data Acquisition (CDA) 
stations. The CDA stations relay the data to the National Environmental Satellite, 
Data and Information Service (NESDIS), located in Suitland, Maryland, for 
processing and distribution.

As a result of the design of the AVHRR scanning system, the normal operating mode 
of the satellite calls for direct transmission to Earth (continuously in 
real-time) of AVHRR data. This direct transmission is called HRPT (High Resolution 
Picture Transmission). In addition to the HRPT mode, about 11 minutes of data may 
be selectively recorded on board the satellite for later playback. These recorded 
data are referred to as LAC (Local Area Coverage) data. LAC data may be recorded 
over any portion of the world, as selected by NOAA/NESDIS, and played back on the 
same orbit as recorded or during a subsequent orbit. LAC and HRPT have identical 
Level 1b formats.

The full resolution data are also processed on board the satellite into GAC 
(Global Area Coverage) data which are recorded only for readout by NOAA's CDA 
stations. GAC data contain only one out of three original AVHRR lines. The data 
volume and resolution are further reduced by averaging every four adjacent samples 
and skipping the fifth sample along the scan line.

POES satellites operate in relatively low orbits, ranging from 830 to 870 km above 
the earth. They circle the earth approximately 14 times per day (with orbital 
periods of about 102 minutes). The orbits are timed to allow complete global 
coverage twice per day, per satellite (normally a daytime and a nighttime view of 
the earth) in swaths of about 2,600 km in width. High resolution (1 kilometer) 
data are transmitted from the satellite continuously, and can be collected when 
the satellite is within range of a receiving station. Recorders on board the 
satellite are used to store data at a 4 kilometer resolution (processed by the 
on-board computers) continuously, and a limited amount of data at a 1 kilometer
resolution on demand. The recorders are dumped when the satellite is within range 
of a NOAA receiving station.


4.0  DATA FORMAT AND FILE NAMING

4.1  File Naming conventions

NSS.HRPT.NM.D06080.S0433.E0442.B1942626.WI.L6592061

where:
 HRPT is the data type
 NM is the satellite (M)
 D06080 is the year (06) and Julian day (080)
 S0433 is the scan start time (UTC)
 E0442 is the scan end time (UTC)

4.2  Data Format
 
These data are in Level 1-b format.

Complete information on the NOAA POES AVHRR format is available from
the NOAA KLM User's Guide:

http://www2.ncdc.noaa.gov/docs/klm/

AVHRR Level 1b data are present as a collection of data sets. Each data set 
contains data of one type for a discrete time period. Thus, for AVHRR, there 
are separate HRPT, LAC, and GAC data sets. Time periods are arbitrary subsets of 
orbits, and may cross orbits (i.e., may contain data along a portion of an 
orbital track that includes the ascending node, the reference point for counting 
orbits). Generally, GAC data sets are available for corresponding time periods 
and usually have a three to five minute overlap between consecutive data sets. 
Level 1b (following FGGE terminology) is raw data in 10 bit precision that have 
been quality controlled, assembled into discrete data sets, and to which Earth 
location and calibration information has been appended, but not applied. Other 
parameters appended are: time codes, quality indicators, solar zenith angles, 
and telemetry.


5.0  DATA REMARKS


6.0  REFERENCES


None.