Want to give Aspen a test drive? It comes with sample data files, located in the Sample Data/ directory (found below the Aspen installation directory).
Aspen (Atmospheric Sounding Processing ENvironment) is used for analysis and quality control (QC) of sounding data. It has the following capabilities:
- Automatically apply quality control procedures to the sounding data
- Present data in tabular and graphical forms
- Automatically determine levels and code them in WMO message formats
- Transmit the WMO messages to other systems
- Save the raw and derived data products in various formats
- View multiple soundings in a synoptic map interface
Since Aspen can process data provided in the AVAPS “D” file, Vaisala MW41, NCAR GLASS, NCAR MCASS, NCAR CLASS, and generic CSV formats, it is able to analyze both dropsonde and upsonde soundings.
Aspen is designed to operate as automatically as possible, while allowing the user to have some control over the QC methods. For instance, as soon as the user selects a sounding file for processing, the data is brought into Aspen and automatically analyzed. In most cases this first pass will be the only one required. If the processing needs to be modified, the user can change the QC parameters and reprocess the data as many times as necessary.
An extensive series of QC algorithms are applied to the data. These algorithms typically have one or two parameters that may be adjusted by the user if the default values are not suitable for a particular sounding. The user can save the modified options, so that when a new sounding is opened, the initial analysis will use the customized QC parameters.
Aspen is designed so that its operation requires minimal user intervention. However, there are a few concepts that are very helpful in understanding the behavior of the program.
The QC process mainly removes suspect data points
Aspen maintains two separate data sets: the raw data and the QC data. At the start of processing, the QC data is an exact copy of the raw data. The algorithms are then successively applied to the QC data. As the processing proceeds, data points that fail each test are removed from QC data set. At the end of this process, a final smoothing is applied to the remaining QC data. It is important to understand that most of the QC steps simply remove unreliable points from the raw data set. The dynamic adjustments and the final smoothing are the only steps where the observed data values are actually modified.
Time is the independent variable
A sounding is simply a time series of observations, and so almost all of the QC operations are based on the time of each data point. The QC parameters are specified in relation to time, and the tabular data listings are ordered by time.
The processing follows a fixed sequence
The complete processing routine is applied as soon as a sounding is selected for analysis, and whenever the user chooses to recompute the analysis. The sequence is as follows:
- Apply the QC algorithms, discarding bad points and applying corrections
- Compute the levels, by analyzing the QC results.
- Code the WMO message, using the levels as input.
Edit meThroughout this manual, notes in italics provide additional information and suggestions which, while not essential to operation, will help you use Aspen more effectively.