Global Hydrology Resource Center(GHRC) is one of NASA's Earth Science Data Centers and is a collaboration between MSFC and University of Alabama in Huntsville.

GPM Ground Validation DC-8 Nadir-Oriented Camera GCPEx

Table of Contents

Introduction
Campaign
Instrument Description
Investigators
File Naming Convention
Data Format
Citation
Contact Information

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 https://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: ghrcdaac@itsc.uah.edu
Web: http://ghrc.nsstc.nasa.gov/