Title: AVHRR Visible Band Calibration / Intercalibration (for Climate Studies)
1AVHRR 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
3Why 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.
4Why 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
5Goals 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.
7Proposed 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/
8Example 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
9Example 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.
10Example 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.
11ORA (C. Cao and others) has automated SNOs from
AVHRR, AMSU and HIRS and offers a real-time
monitoring capability.
12A 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
13Ch1 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.
14Comparison 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)
15Testing 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
16Testing 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.
17Conclusions
- 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).