MISR Ancillary Radiometric Product (ARP)
Processing Summary Page
Last update: July 10, 2001

Contents

• Calibration Experiment Timeline
• ARP algorithm basis and change log
• ARP's: [Active] [Inactive]
• G1 coefficients
• G1 trend plot for active ARPs
• Radiance calculations versus ARP
• Internal memorandum
• Contact information

Overview

The purpose of this page is to provide technical information, to the MISR science community, as to the status of the radiometric performance of the MISR cameras. An on-orbit experiment is conducted at bi-monthly intervals. At this time a diffuse panel reflects solar light into the cameras. The intensity of this light is measured with our on-board photodiodes, that is we utilize "detector-based" standards.With measured camera output DN and known incident radiances, we can compute radiometric calibration coefficients as a funtion of time in orbit. The coefficients are packaged into a file called the Ancillary Radiometric Product (ARP), and delivered to our data processing center, following each calibration. The information below tells you more about the algorithms used to produce these coefficients, how these algorithms have been changed over the mission life, and which file is currently being used in data processing. The site assumes the reader has an insiders view of the calibration experiment concept. More informaiton can be obtained from the calibration literature, or by contacting the MISR Calibration Scientist.

Ideally each investigator desires to have a data products derived from the best-available ARP coefficient file. To determine which ARP file was used to develop a given data product, you would use an HDF browser, such as HDF_Scan. (A unix-based procedure will also supply this information.) Read the metadata: annotation text that is part of the data file. Under Annotation Text: Input Data files, find the ARP version number used to produce your data, then compare it to the latest delivered ARP file that has been produced for that data acquisition date Active ARP section, below. If these files match, then you have most current version of the radiometric calibration file. If the files have not been constructed using the best-available, a crude adjustement of your data can be make by following the procedure below.

As of this date in time there are still some outstanding calibration issues to be resolved. The current ARP files for some of the time periods (T2-T5) have coefficients which cause the An Red-NIR bands to be 3% brighter than we believe is actually the case. Additionaly, the fore-aft camera radiances are biased by a few %. These errors are small, and will be corrected in new ARP files to be delivered later this summer. Until that time requesting that data products be re-processed is not recommended.

Calibration Experiment Timeline
(Orbit numbers and An times from IOT web page,
http://osa.jpl.nasa.gov/MISR_Project/ops/im/activities/miact.html)

Algorithm basis

References:

Algirithm change log:

Active ARPs

(1) SCF Directory: /data/bank/anc/ARP_INFLTCAL/database/MISR_AM1_ARP_INFLTCAL_*.hdf
(2) The date first used is the same as the time range start for usage of this file

Inactive ARPs

An inactive ARP is one that is no longer in use for MISR data product generation. These files have been superceded by the active files listed below.

(1) SCF Directory: /data/bank/anc/ARP_INFLTCAL/database/MISR_AM1_ARP_INFLTCAL_*.hdf

Channel mean coefficients
(for both active and inactive ARPs)

The 3/9/01 unreleased files would, if delivered to the DAAC, replace T002_0005, T003_0001, and T004_0001. They lower radiances in the An Red and NIR by about 3%. They will not be delivered to the DAAC, however, as several algorithm changes are planned before final production of these files.

• Trend plot for active ARP values (currently used in production)
• Trend plot for current SCF files (not in production)

Radiance calculations versus ARP

Linear model

A few investigators may wish to determine radiances that would have been computed if a specific ARP had been used in the L1B1 or L1B2 data production. As an example, say that a L1B2 data product was produced with ARP T002_0004, but it is now recommended that ARP T002_0005 be used for that data acquisition time period but the reprocessing has not yet occurred. This is a simplified case in that the G0 and G2 coefficients were set to zero for both these file.

We will define the ARP coefficients that were used in the data processing as G1_old coefficient, and the coefficients we wish had been used as G1_new. Since the MISR radiances are computed using

DN = G1_old * L_old

L_new = G1_old * L_old/ G1_new

One merely looks up the coefficients from the above tables to make the conversion. Note that there are some fine scale pixel-to-pixel corrections that will not be taken into account with this simplified algorithm. There are on the order of 1%. To make corrections to this level of accuracy, the data must be reprocessed.

In our example

G1_old(An_blue) = 22.5434
G1_new(An_blue) = 20.4269
therefore
L1_new=L1_old * 1.10

That is, there is a 10% increase in the radiance with the ARP update. This process will have to be repeated for each of the 36 channels.

Quadratic model

Beginning with ARP T8 a constrained quadratic has been used in our calibration equation. To convert the radiance values from one set of coefficients to another, a more generic equation is needed. The conversion for these files is:

DN = G0_old + G1_old * L_old + G2_old * L_old * L_old

L_new = -2[G0-DN]/{G1 + sqrt(G1*G1 - 4*G2*(G0-dn))}

The above equation is a variant to the usual quadratic inversion. It is preferred for instances where G2 is small.

Reference documents

• SDFM251, Early mission sensor degradation
• Data Quality Statement for ARP- T007, March 7, 2001
• SDFM240, ARP T002_0005 release
• SDFM231, OBC performance
• SDFM230, ARP T002_0004 release
• SDFM229, Diode Response
• SDFM228, ARP T002_0003 release

Contact information

URL: http://www-misr.jpl.nasa.gov/mission/valwork/val_reports/arp.html
Author: Carol.J.Bruegge@Jpl.nasa.gov