AVHRR Visible Band Calibration / Intercalibration (for Climate Studies)
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AVHRR Visible Band Calibration / Intercalibration (for Climate Studies). Andrew Heidinger and Michael Pavolonis * Changyong Cao, Aleksandar Jelenak, Jerry Sullivan, Fred Wu NOAA/NESDIS Office of Research and Applications *Cooperative Institute for Meteorological Satellite Studies (CIMSS)

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AVHRR Visible Band Calibration / Intercalibration (for Climate Studies)

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AVHRR Visible Band Calibration / Intercalibration (for Climate Studies)

Andrew Heidinger and Michael Pavolonis*

Changyong Cao, Aleksandar Jelenak, Jerry Sullivan, Fred Wu

NOAA/NESDIS Office of Research and Applications

*Cooperative Institute for Meteorological Satellite Studies (CIMSS)

Madison, Wisconsin

2nd CORP Science Symposium – Madison Wisconsin, July 13, 2005


  • Background

  • This effort is part of much larger effort within ORA. ORA has funded the AVHRR reprocessing as a pilot project for Scientific Data Stewardship (SDS) – thank you!

  • We hope to continue as a funded project under the NESDIS SDS initiative.

  • ORA now has the entire GAC archive (1979-present; 32 TB) from CLASS.

  • For the first time, we have demonstrated the ability to reprocess this data within ORA. So far we have generated time-series of GVI-x and PATMOS-x. Polar Winds and SST projects are also underway.

  • A large part of this effort is to improve the quality of the AVHRR data and this involves both reflectance and thermal calibration and geolocation.

PATMOS-x

GVI-x

Polar Winds

SST


Why use the The AVHRR for Climate Studies

The Advanced Very High Resolution Radiometer (AVHRR) was launched in the 1979 for non-quantitative cloud imagery and SST. It flies on the NOAA Polar Orbiting Satellites (POES)

2. AVHRR provides enough spatial resolution (1 or 4 km) to resolve many atmospheric and surface features

1. AVHRR Provides enough spectral information for several applications

3. Combined with its long data record (1981-2012) make the 5-channel AVHRR data-set the best we have for decadal studies for many key climate parameters.


Why Improve the AVHRR Reflectance Calibration?

  • Without onboard calibration, the prelaunch reflectance calibrations can be many % in error. Accurate reflectances are critical for cloud, aerosol and vegetation climate records.

  • Analysis of existing post-launch calibrations (esp those use at NESDIS) has shown room for improvement for climate use

  • The calibration of many of the early and the morning orbiting AVHRRs has received little attention

  • New sensors with onboard calibration and new processing techniques (SNO) warrant a new look at this issue.

  • There is still disagreement in the AVHRR reflectance calibrations from different techniques (see right)

D.R. Doelling, 2001: Proceedings AMS 11th Conference on Satellite Meteorology and Oceanography, Madison, Wisconsin, October 15 – 18, pp. 614-617


Goals of this Work

  • Improve upon the existing AVHRR reflectance calibrations for ORA climate work

  • Derive a new self-consistent set of calibrations for whole series of AVHRR data (NOAA-6,7,8,9,10,11,12,14,15,16,17,18,…) that allows for meaningful climate work.

  • Try and build a consensus calibration through multiple collaborations and transfer these new calibrations to the community.


  • My Reflectance Calibration Background

  • Starting working on AVHRR in 1999.

  • Collaborated with Nagaraja Rao and Jerry Sullivan on extending N. Rao’s Libyan Desert Technique to NOAA-12 (a morning satellite).

    • Heidinger, A. K., J. T. Sullivan and N. Rao, 2003: Calibration of visible and near-infrared channels of the NOAA-12 AVHRR using time-series of observations over deserts.I.J.R.S., 24, 3635-3649.

  • After death of N. Rao, Mike Weinreb asked that I develop initial post-launch calibration for NOAA-16 (a dual gain instrument). Worked with C. Cao on the first SNO’s and wrote the following paper.

    • Heidinger, A. K., C. Cao, and J. T. Sullivan, Using Moderate Resolution Imaging Spectrometer (MODIS) to calibrate advanced very high resolution radiometer reflectance channels, J. Geophys. Res., 107(D23), 4702, doi:10.1029/2001JD002035.

  • Fred Wu (formerly of CIMSS) was later hired for AVHRR calibration and I am now only interested in the calibrations for climate work.


Proposed Methodology – Simultaneous Nadir Observations (SNO)

  • Our goal is to use Simultaneous Nadir Observations (SNO) to improve both the relative and absolute calibration. This method provides new information and constraints not used in past studies,

  • Polar orbiting satellites intersect each other at high latitudes. This occurs for satellites even in very different orbits.

  • We have primarily analyzed MODIS and AVHRR SNO data though could do VIRS, ATSR and geo imagers.

  • We also study AVHRR to AVHRR SNO’s to fix the relative calibration from one instrument to another.

Taken from Changyong Cao: http://www.orbit.nesdis.noaa.gov/smcd/spb/calibration/intercal/


Example Imagery from a SNO

Sensor #1 data projected on to Sensor #2 strip. These points comprise the SNO

± 5° Nadir Strip from Sensor #1

± 5° Nadir strip from Sensor #2


Example of one July’s SNO’s for ch1 and ch2 of TERRA and NOAA-16

(note y-axis should be ch1 not ch2 on left-hand plot)

SNO’s from MODIS and AVHRR allow us to transfer MODIS’s calibration to the AVHRR directly.


Example of SNO’s for one month of PATMOS-x data (July 1992)

For July 1992, NOAA-11 and NOAA-12 gave 78 grid-cells that met SNO criteria. Note dark counts are removed so line should pass through origin.

This data provides a constraint on the ratio of NOAA-11 to NOAA-12 calibration slopes. Does not provide any information on absolute calibration by itself.


ORA (C. Cao and others) has automated SNO’s from AVHRR, AMSU and HIRS and offers a real-time monitoring capability.


A New Libyan Desert Reference for pre-MODIS Calibration

In addition to SNO data (AVHRR/MODIS and AVHRR/AVHRR), we also employ a New Libyan Desert Reflectance Reference value to provide an estimate of the absolute calibration for the afternoon satellites.

  • This new Libyan Reflectance Reference was constructed using the following steps:

  • Selection of Stable Target (Used same as N. Rao)

  • Acquisition of MODIS data over Target

  • BRDF modeling

  • Spectral Adjustment due to Water Vapor (MODIS + MODTRAN)

  • Spectral Adjustment from Hyperion data

This method gives us the absolute calibration

for the pre-MODIS AVHRR data.

MODIS TRUE COLOR


Ch1 Calibration Slopes from All Satellites and All Methods

  • Reflectance = Calibration Slope x ( Count – Dark Count)

  • Note the relative agreement between the calibration slopes derived from different methods.


Comparison of Ch 1 Equations for NOAA-7,9,11,14,16

14

9

7

11

16

RCS = Rao, Chen and SullivanVS = Vermote and El Saleous

TC = Tahnk and CoakleyWU = Fred Wu (Operational NOAA)


Testing the New Reflectance Calibrations

  • Because the ORA effort also involves generation of climate products, we can test the impact of new calibrations on climate records.

  • Aerosol optical depths should test the consistency of the low end

Testing Long Term Consistency

Testing Absolute Accuracy

AOT Tables from A. Ignatov


Testing the Consistency for bright scenes

  • Greenland’s Reflectance should be stable and tests the high end stability

  • Need to compare to absolute standards published by Tahnk and Coakley.


Conclusions

  • ORA is undertaking activity to improve the AVHRR 1b data. An efforts are underway to communicate these improvements to the wider community through metadata / ancillary files.

  • We are seeking a consensus calibration and are seeking collaborators currently working with El Saleous and Vermote from NASA.

  • Using the SNO technique, we can transfer MODIS’s calibration directly to the AVHRR

  • SNO’s also provide a direct method to ensure reflectance continuity across AVHRR transitions without assumptions about vicarious targets.

  • SNO’s coupled with a new MODIS-based vicarious desert calibration target appear to have produced an AVHRR reflectance calibration that is consistent for all AVHRR’s (and is consistent with MODIS).


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