CHAPTER 9 SECTIONS > File Description | File Content
The IAS is responsible for the sustained radiometric and geometric calibration
of the Landsat 7 satellite and ETM+ and passing this knowledge to the
user community. This is achieved by assessing new imagery on a daily basis,
performing both radiometric and geometric calibration when needed, and
developing new processing parameters for creating level 1 products. Processing
parameters are stored in the Calibration Parameter File (CPF) which is
stamped with applicability dates and sent to the LP-DAAC for storage
and eventual bundling with outbound Level 0R products. The CPF is also
sent to international ground stations via the Landsat 7 Mission Operations
9.1.1 Calibration Parameter File Updates
IAS updates and distributes the calibration parameter file at least every
90 days. Updates will likely be more frequent during early orbit checkout
and will also occur between the regular 90-day cycles whenever necessary.
Irregular updates, however, will not affect the regular 90 day schedule.
The timed release of a new calibration parameter file must be maintained
because of the UT1 time corrections and pole wander predictions included
in the file. These parameters span a 180 day interval time centered on the
effective start date of the new IAS CPF. A CPF archive is maintained by
the IAS. At this web
site, you can download and view all CPFs since launch.
The calibration parameter file is time stamped by IAS with an effective
date range. The first two parameters in the file, Effective_Date_Begin
and Effective_Date_End, designate the range and are of the form YYYY-MM-DD.
The Effective_End_Date for the most recent parameter file is its Effective_Date_Begin
plus 90 days. After this date the file is without applicable UT1 time
predictions. The parameter file that accompanies an order has an effective
date range that includes the acquisition date of the image ordered.
File Naming Conventions
Through the course of the mission, a serial collection of CPFs is generated
and sent to the LP-DAAC for coupling to 0R products. A distinct probablity
exists that a CPF will be replaced due to improved calibration parameters
for a given periord or perhaps due to file error. The need for unique
file sequence numbers becomes necessary as file contents change. The following
file naming procedure is used by IAS to name the CPF:
|| L7 = Constant for Landsat 7
CPF = 3-letter CPF designator
yyyy = 4-digit effectivity starting year
mm = 2-digit effectivity starting month
dd = 2-digit effectivity starting day
_ = Effectivity starting/ending date separator
yyyy = 4-digit effectivity ending year
mm = 2-digit effectivity ending month
dd = 2-digit effectivity ending day
nn = Sequence number for this file
As an example, suppose four calibration files were created by the IAS
on 90-day intervals and sent to the LP-DAAC during the first year of
the mission. Further suppose that the first file was updated twice and
the second and third files were updated once. The assigned file names
would be as follows:
It is worth noting the 00 sequence number assigned to the original
CPF. This reserve sequence number uniquely identifies the pre-launch
CPF. Sequence numbers for subsequent time periods all begin with 01.
New versions or updates are incremented by one.
This example assumes the effectivity dates do not change. The effectivity
date range for a file can change, however, if a specific problem (e.g.
detector outage) is discovered somewhere within the nominal 90-day effectivity
range. Assuming this scenario, two CPFs with new names and effectivity
date ranges are spawned for the time period under consideration. The effective_date_end
for a new pre-problem CPF would change to the day before the problem occurred.
The effective_date_begin remains unchanged. A post-problem CPF with a
new file name would be created with an _effective_date_begin corresponding
to the imaging date the problem occurred. The effective_date_end assigned
would be the original effective_date_end for the time period under consideration.
New versions of all other CPFs affected by the erroneous parameter also
would be created.
Using this example, suppose a dead detector is discovered to have occurred
on January 31, 1999. Two new CPFs are created that supersede the time
period represented by file number three, version 2, and a new version
of file number four is created. The new file names and sequence numbers
All calibration parameters are stored as American Standard Code for
Information Interchange (ASCII) text using the ODL syntax developed by
JPL. ODL is a tagged keyord language developed to provide a human-readable
data structure to encode data for simplified interchange. The body of
the file is composed of two statement types:
- Attribute assignment statement used to assign values to parameters.
- Group statements used to aid in file organization and enhance parsing
granularity of parameter sets.
To illustrate consider the first three parameters in the file: Effective_Date_Begin,
Effective_Date_End, and the CPF_File_Name. These three parameters form their
own group which is called FILE_ATTRIBUTES. The syntax employed for this
collection of parameters in the CPF appears as:
|GROUP = FILE_ATTRIBUTES
||Effective_Date_Begin = 1999-02-26
Effective_Date_End = 1999-05-26
CPF_File_Name = L7CPF19990226_19990526.01
| END_GROUP = FILE_ATTRIBUTES