5. Current Research
In this section, we highlight some recent research achievements of the
Division. More detailed summaries are contained in the Division's
bi-annual Reports.
Sensor Physics Branch
Powerful New Tool for Inter-satellite Instrument Calibration
A powerful method has been developed to quantify the inter-satellite calibration
biases for radiometers on polar-orbiting satellites. The method is based on
Simultaneous Nadir Overpass (SNO) observations. An SNO occurs when the nadir points
of two polar-orbiting satellites cross each other within a few seconds. Such
crossings occur at the orbital intersections of the satellites in Polar Regions.
At each SNO, radiometers from each pair of satellites view the same place at the
same time at nadir, thus eliminating uncertainties associated with the atmospheric
path, view geometry, and time differences. Their measurements should be identical.
By comparing the measurements of the two satellites during SNOs, it's possible to
determine the bias of one instrument with respect to the other.
The SNOs allow us to resolve small calibration biases at or below the combined
instrument noise for many channels (Figure 2).
Figure 2: Intersatellite radiance biases between HIRS on NOAA-15 and -16 show
excellent agreement with uncertainties below the combined instrument noise.
It also shows that seasonal variations in the bias are highly correlated with
the lapse rate, indicating small spectral response differences between satellites.
The Next Generation Microwave Integrated Retrieval System (MIRS)
To prepare for future NPOESS microwave instruments such as CMIS and ATMS, SMCD has
begun development of the next generation retrieval system - the microwave integrated
retrieval system (MIRS). This physically-based system will derive the profiles of
atmospheric parameters such as temperature, water vapor, and cloud hydrometeors
over land and oceans by using the measurements from the microwave imager and
sounder. An advanced radiative transfer model including atmospheric and surface
scattering and polarization is being developed and integrated as part of the
MIRS. With the microwave surface emissivity model developed by SMCD, water vapor
and cloud water can be also retrieved over land. These advanced RT models will
enable combined use of microwave window and sounding channels to simultaneously
derive the cloud water profiles in addition to temperature and water vapor
profiles. This integrated approach will lead to more robust advanced microwave
products from current and future satellite microwave instruments having both
imaging and sounding channels.
Figure 3: Flowchart of microwave integrated retrieval (MIR) system developed
for future NPOESS era sensors such as ATMS and CMIS. The core module describes
the retrieval procedures.
The 2004 Antarctic Ozone Hole
SMCD scientists, working closely with scientists at NOAA's
Climate Prediction Center, continue to closely monitor the Antarctic ozone
hole. Extensive ozone depletion was again observed over Antarctica during
the Southern Hemisphere winter/spring of 2004, with widespread total ozone
anomalies of 45 percent or more below the 1979-1986 base period. The area
covered by extremely low total ozone values of less than 220 Dobson Units,
defined as the Antarctic "ozone hole" area, in September reached maximum
size of greater than 19 million square kilometers, with an average size
in September of 17.4 million square km, smaller than most recent years.
Carbon Cycle Science: An Emerging Product Suite
Working with collaborators at University of Maryland, Baltimore County
(UMBC), SMCD investigators have shown that CO is a robust and useful
product from AIRS. An example of the AIRS CO product for a single day is
shown in Fig. 5. CO is important because it is a component of air pollution,
is a measure of biomass burning, and contributes to the greenhouse effect.
In addition to CO, SMCD is also developing algorithms for deriving other
carbon cycle products, such as CO2 and CH4, from advanced IR sounders.
Figure 5: Global CO distribution at 500 mb derived from Aqua AIRS (9/29/2002)
