CAMEX-3: Airborne Vertical Atmosphere Profiling System (AVAPS)

Table of Contents

1. Introduction
2. Content and structure of the AVAPS files
    2a. Browse Images: 98264.1850_avaps_plot.gif
    2b. Raw Data: 98264.1850_avaps_raw.txt
    2c. Quality Controlled data: 98264.1850_QC.cls.txt
    2d. NetCDF files: 98264.1850_QC.cdf
3. Contact Information

1. Introduction

The Airborne Vertical Atmosphere Profiling System (AVAPS) uses dropwindsonde and Global Positioning System (GPS) receivers to measure the atmospheric state parameters during the its descent. Dropwindsondes measure vertical profiles of pressure, temperature, humidity, and wind during their descent through the atmosphere. During CAMEX-3, the AVAPS system was deployed on the NASA DC-8 aircraft. There were over one hundred dropwindsondes released during the experiment, with 39 released on one flight alone.

Vertical measurement of the atmosphere goes back many decades with the current dropwindsonde coming into being in 1993. Working in collaboration with the National Oceanic and Atmospheric Administration/ Atlantic Oceanographic and Meteorological Laboratory (NOAA/AOML) and the German Aerospace Research Establishment (DLR), the National Center for Atmospheric Research/ Atmosphere Technology Division (NCAR/ATD) developed a third-generation dropwindsonde using a new sensor module and a GPS receiver from Vaisala, Inc. More accurate wind profiles are now available because of a NCAR/ATD-developed, unique square-cone parachute that reduces the initial shock load and stabilizes the dropwindsonde as it falls. The dropswindsondes are the responsibility of NCAR/ATD/Surface and Sounding Systems Facility who provided the final post experiment quality control processing. For more information about the AVAPS system, see: http://ghrc.msfc.nasa.gov/camex3/instruments/avaps.html.
Additionally, the Vaisala page details the system at http://www.vaisala.com/, and the GPS dropsonde page at ATD at http://www.atd.ucar.edu/sssf/facilities/dropsonde/gpsDropsonde.html.

2. Content and structure of the AVAPS files

There are four files associated with each dropwindsonde released during the experiment: a GIF image of the sounding, a raw data .txt file, a QCed data file, and finally a NetCDF file. Each of these will be discussed below. The naming convention for the files is typical of the CAMEX-3 file structure: for example, 98264.1850_avaps_[suffix], where the suffix further delineates the type of file. The first five digits, 98264 represents yyddd with ddd representing the day of the year. Following the 'avaps' identifier are one of four suffixes which are explained below.

2a. Browse Images: 98264.1850_avaps_plot.gif

The suffix 'plot.gif' identifies this browse image as a plotted sounding in GIF format. The skew-T diagram shows the temperature, dewpoint, and vertical wind profiles measured during the flight of the dropwindsonde. Date, time of release, and mission ID are given in the title of the image. An example of the sounding image is shown below:

2b. Raw Data: 98264.1850_avaps_raw.txt

This file contains the raw data as relayed from the dropwindsonde to the aircraft. Data is in ASCII form. It has not been QCed, and usually contains many extraneous points.

A sample is shown below. For the purpose of this document, this data has been formatted to appear as shown. One simple way to obtain neatly aligned data is to import the raw data text file into a spreadsheet (e.g. Excel)  for automatic formatting. Close examination will reveal that the file reads forward in time from the top of the file to the bottom, consequently pressures increase from top to bottom.
 
 

2c. Quality Controlled data: 98264.1850_QC.cls.txt

This is the data file as it appears following quality control by NCAR. These data are very similar in initial appearance to the raw data. One noteable exception is that the data is 'inverted', that is, the data has been reformatted so that the surface data (the last sensed by the sonde) appears first while the data collected at the aircraft flight level appear last. Note also that the times run backwards as you read the dataset from the top to bottom. This puts the data into a form very similar to that used by radiosonde (i.e. surface launched) instruments for ease in reading by existing radiosonde software packages. The last six data fields are all empty (denoted by the filler '99?'), as these data are the parameters reported from the surface during the surface launched radiosonde flight.
 
 

2d. NetCDF files: 98264.1850_QC.cdf

NetCDF (network Common Data Form) is an interface for array-oriented data access and a library that provides an implementation of the interface. The netCDF library also defines a machine-independent format for representing scientific data. Together, the interface, library, and format support the creation, access, and sharing of scientific data. The netCDF software was developed at the Unidata Program Center in Boulder, Colorado. The freely available source can be obtained as a compressed tar file or a zip file from Unidata [http://www.unidata.ucar.edu/packages/netcdf/] or from other mirror sites.

Examining the data using one of the NetCDF utilities mentioned at the above site, values for measured parameters (e.g. temperature, relative humidity) as well as derived/calculated parameters (e.g. vertical distance between data reports, theta, theta-e) are given. Depending upon the utility, output can be either tabular or graphical.
 
 
 

3. Contact Information

Data can be ordered and questions addressed at http://ghrc.nsstc.nasa.gov/.

To order this 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: ghrc@eos.nasa.gov

---

NASA Information Contact: Michael Goodman, Global Hydrology and Climate Center GHRC Web Curator: GHRC Web Team Last update: Tuesday, 12-Jun-2007 10:24:18 CDT If you have trouble viewing or navigating this page, please contact GHRC User Services. U.S. Government Compliance report.