For more information, please refer to: Wimmers, A. J., C. S. Velden, 2011: Seamless Advective Blending of Total Precipitable Water Retrievals from Polar-Orbiting Satellites. J. Appl. Meteor. Climatol., 50, 1024-1036. doi: http://dx.doi.org/10.1175/2010JAMC2589.1
In MIMIC-TPW, a data-blending technique combines disparate swaths of
microwave observations from polar orbiting satellites in order to
create near-seamless animations of advecting radiance features. It
builds off of the methods used in MIMIC-TC
which depicts microwave imagery of tropical cyclones in regular time
(Wimmers and Velden, 2007).
MIMIC-TPW was originally developed as an experimental, near real time
visualization tool utilizing microwave-derived moisture fields to
follow the development and progression of cyclone-spawning easterly
waves and the cyclone-impeding Saharan Air Layer in the North Atlantic
Ocean. It has since been expanded to operate globally, with finer-resolution displays to fit the needs of our end-users. In this stage of development, we continue
to make product modifications and improvements as we monitor the
MIMIC-TPW uses retrieved total precipitable water values based on an
algorithm developed by Alishouse et al. (1990),
which derives these values from a linear function of 19, 22
and 37 GHz brightness temperatures available
from passive microwave sensors aboard several polar orbiting satellite
platforms. We currently use real-time data from the SSM/I sensor on the
DMSP-13/14 satellites and the AMSR-E sensor on the Aqua satellite.
Other options are not employed at this time because of our product's
sensitivity to biases between different retrievals of TPW and
3. Swath advection
All TPW data must be processed so that they can be used concurrently at
display times of the MIMIC-TPW product. To represent TPW at times
several hours away from the retrieval time, we treat TPW as a purely
conservative tracer advected by a lower-tropospheric mean layer wind
using fields from the GFS global model. For example,
the following DMSP/SSMI data swath crossed through the North
Atlantic basin at approximately 1015
UTC (3 Sept 2004):
In the MIMIC-TPW algorithm, this swath is then advected backward and
forward in time using the mean layer wind field in order to create
synthetic hourly data
corresponding to the original swath:
The mean layer wind field is commensurate in depth with the majority of
columnar moisture over the tropical oceans (between 600 hPa and the
Because the MIMIC-TPW product
is real-time, we use forecast wind fields as well as analysis winds.
However, over time the "older" advections in the dataset are recomputed
as analysis winds come in to replace forecast winds.
Currently, we generate this synthetic hourly data for all times on the
hour between +/- 16 hours from observation time of each swath. Thus for
a given hour, a domain such as the North Atlantic basin has 20-30
synthetic swaths of data from which our algorithm can create a nearly
complete composite image.
The final product is a simple composite of many advected TPW swaths
over a selected domain.
Every pixel on the final composited image is a time-weighted average
synthetic data originating from the shortest timespans before and after
the image time.
The TPW retrieval algorithm does not produce TPW values over land.
Without any further
adjustments, the final product as described so far would show "shadows"
of islands and continents advecting into the oceans. In order to
eliminate these shadows, we apply an interpolation/extrapolation
technique based on Bertalmío et al. (2000). The TPW retrieval
algorithm also does not produce values in pixels with suspected
precipitation. However, for our visualization purposes, we fill in
these data gaps with high TPW values.
As stated above, this technique is highly sensitive to biases between
the different satellite instruments' calibration and/or retrievals of
TPW. Even slight
differences between retrievals can create two easily discernable
in the animation: 1) The appearance of data swath edges throughout
the image domain, and 2) The apparent "pulsing" of
various high-TPW areas, especially in areas of precipitation.
Bertalmío, M., A. Bertozzi, G. Sapiro, 2001: "Navier-Stokes,
and Video Inpainting"
, IEEE CVPR 2001, Hawaii, USA.
Alishouse, J., S. Snyder, J. Vongsathorn, and R. Ferraro, 1990: Determination of oceanic total precipitable water from the SSM/I, IEEE Trans. Geosci. Remote Sens., 28
Wimmers, A. J. and C. S. Velden, 2007: MIMIC: A new approach to
visualizing satellite microwave imagery of tropical cyclones. Bull. Amer. Meteor. Soc., 88
Created by Tony Wimmers and Chris Velden
Cooperative Institute for Meteorological Satellite Studies (CIMSS)
University of Wisconsin - Madison
Updated November, 2011