GPM Ground Validation DC-8 Nadir-Oriented Camera GCPEx
Table of Contents
Introduction
The GPM Ground Validation DC-8
Nadir-Oriented Camera data set contains geolocated visible wavelength
imagery of the ground obtained over Ontario, Canada during the GCPEx
campaign. The data was collected on a cloud free flight day (February
20, 2012) in order to measure surface emissions. Therefore, this data
set may be useful in determining snow cover and lake ice cover for
emissivity studies in conjunction with CoSMIR data, for example. In
addition, aircraft navigation information are included in the data set
files for convenience and reproducibility. Finally, ground temperature
measurements are also included in the files to aid in emissivity
retrievals.
Campaign
The GPM Cold-season Precipitation Experiment (GCPEx)
occurred in Ontario, Canada during the winter season of 2011-2012.
GCPEx addressed shortcomings in the GPM snowfall retrieval algorithm by
collecting microphysical properties, associated remote sensing
observations, and coordinated model simulations of precipitating snow.
These data sets were collected to aid in the achievement of the over
arching goal of GCPEx which is to characterize the ability of
multi-frequency active and passive microwave sensors to detect and
estimate falling snow.
Further details on GCPEx are available at http://gpm.nsstc.nasa.gov/gcpex. Information on the Global Precipitation Measurement (GPM) mission is available at http://pmm.nasa.gov/GPM.
Instrument Description
The GPM Ground Validation nadir-looking
camera imagery was recorded by an Axis 223M network camera. This
commercially available camera has the following specifications:
Image sensor: 1/2.7" Progressive scan RGB CCD
Lens: 4.0-8.0 mm
F1.4, DC-iris, C mount
Angle of view, horizontal: 38 degrees - 72 degrees
Minimum illumination:
Color: 1.5 lux, F1.4; B/W: 0.2 lux, F1.4
Shutter time: 1/7500 s to 2 s
Additional information on the Axis 223M camera can be found at http://www.axis.com/files/datasheet/ds_223m_32713_en_0809_lo.pdf.
During GCPEx, imagery was recorded by
the nadir-looking camera on February 20, 2012, which was a clear air
flight day. The video was recorded at a resolution of 1280x720 pixels
and 30 Hz at the maximum zoom (38 degree field of view). At the DC-8's
average cruising altitude of 10 km and ground speed of 200 m/s, this
provides a nadir resolution of 9.2 meters. Only the central scan of each
frame was processed for geo-location.
Ground temperatures were also measured
with a nadir-pointing infrared thermometer. The measurements were
obtained with the commercially available PRT-5 thermometer. The
specifications for the thermometer can be found at http://www.pyrometer.com/oceantemperature.html.
Investigators
Joe Munchak
University of Maryland / NASA Goddard Space Flight Center
Mail Code: 612
Greenbelt, MD 20771
File Naming Convention
The DC-8 Camera data files are HDF5 (Hierarchical Data Format) and are named with the following convention:
gcpex_nadir_cameraDC8_[YYYYMMDD]_[HHMMSS].HDF
where,
gcpex = GPM Cold-season Precipitation Experiment (GCPEx)
nadir_cameraDC8 = instrument name
YYYY = year
MM = month
DD = day
HH = hours
MM = minutes
SS = seconds
HDF5 =
Hierarchical Data Format
Data Format
Data files are in HDF5 (Hierarchical
Data Format). The files are divided into 15-minute segments to reduce
individual file size. Start time is indicated in the file name. File
contents include RGB byte values for each pixel, timestamps for each
scan, aircraft navigation for every second, and geospatial locations
(latitude/longitude) for each pixel.
Absolute navigation errors of up to 1000
meters are possible when aircraft roll is less than 3 degrees in
magnitude (greater errors may occur during times of greater roll
magnitude). It is recommended to compare imagery to a high-resolution
land/water mask to ensure that geolocation is accurate in the region of
interest.
More information about HDF5 may be found at the HDF group home page.
In addition, read software has been provided by the P.I. to assist in
processing the data. The code for the program can be found at ftp://gpm.nsstc.nasa.gov/gpm_validation/gcpex/dc8_camera_nadir/doc/read_nadircam.pro.
Citation
Our data sets are
provided through the NASA Earth Science Data and Information System
(ESDIS) Project and the Global Hydrology Resource Center (GHRC)
Distributed Active Archive Center (DAAC). GHRC DAAC is one of NASA's
Earth Observing System Data and Information System (EOSDIS) data
centers that are part of the ESDIS project. ESDIS data are not
copyrighted; however, in the event that you publish our data or
results derived by using our data, we request that you include an
acknowledgment within the text of the article and a citation on your
reference list. Examples for general acknowledgments, data set
citation in a reference listing, and crediting online web images and
information can be found at: http://ghrc.nsstc.nasa.gov/uso/citation.html
Contact Information
To order these data or for further information, please contact:
Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: support-ghrc@earthdata.nasa.gov
Web: http://ghrc.nsstc.nasa.gov/
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