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AVHRR Visible Band Calibration / Intercalibration (for Climate Studies)

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Title: PowerPoint Presentation Author: heidinger Last modified by: heidinger Created Date: 3/15/2005 2:20:52 AM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: AVHRR Visible Band Calibration / Intercalibration (for Climate Studies)


1
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
2
  • 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
3
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.
4
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
5
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.

6
  • My Reflectance Calibration Background
  • Starting working on AVHRR in 1999.
  • Collaborated with Nagaraja Rao and Jerry
    Sullivan on extending N. Raos 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 SNOs 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, doi10.1029/2001JD0
    02035.
  • Fred Wu (formerly of CIMSS) was later hired for
    AVHRR calibration and I am now only interested in
    the calibrations for climate work.

7
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 SNOs to fix the
    relative calibration from one instrument to
    another.

Taken from Changyong Cao http//www.orbit.nesdis
.noaa.gov/smcd/spb/calibration/intercal/
8
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
9
Example of one Julys SNOs for ch1 and ch2 of
TERRA and NOAA-16
(note y-axis should be ch1 not ch2 on left-hand
plot)
SNOs from MODIS and AVHRR allow us to transfer
MODISs calibration to the AVHRR directly.
10
Example of SNOs 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.
11
ORA (C. Cao and others) has automated SNOs from
AVHRR, AMSU and HIRS and offers a real-time
monitoring capability.
12
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
13
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.

14
Comparison of Ch 1 Equations for NOAA-7,9,11,14,16
14
9
7
11
16
RCS Rao, Chen and Sullivan VS Vermote and El
Saleous TC Tahnk and Coakley WU Fred Wu
(Operational NOAA)
15
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
16
Testing the Consistency for bright scenes
  • Greenlands Reflectance should be stable and
    tests the high end stability
  • Need to compare to absolute standards published
    by Tahnk and Coakley.

17
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 MODISs
    calibration directly to the AVHRR
  • SNOs also provide a direct method to ensure
    reflectance continuity across AVHRR transitions
    without assumptions about vicarious targets.
  • SNOs coupled with a new MODIS-based vicarious
    desert calibration target appear to have produced
    an AVHRR reflectance calibration that is
    consistent for all AVHRRs (and is consistent
    with MODIS).
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