Introduction

SNDPRO 1.3 is a program used to convert and edit ECC ozonesonde data obtained from a ground station and report the results in several commonly used output formats. It is designed to run under Win9X or NT and accept data from Vaisala Metgraph or T-Max ground stations. The output formats are X-CSV, WMO fixed format, NASA-Ames 2160 and a simple table which has been used informally at AES. In addition to text outputs several graphs are also provided.

Setup

The executable can be run from any suitable directory and a setup file called Sndpro.ini needs to be placed in the system (Windows) directory. All of the configuration involves editing this file.

Sndpro.ini is a standard Windows setup file with each section indicated by a title in square brackets. Any line that starts with ‘;’ is treated as a comment. Most of the sections have clear meanings and adding a new station usually just involves including details of the station such as name and ID number but a few sections require some more explanation.

[Station Elevation] - This section is used when loading a T-Max flight so that GP height can be estimated. For Vaisala flights this is read directly from the ‘Z’ file.

[Station Latitude] - As above

[Station Longitude] - As above

[WMO Station Abbreviation] - The two letter station identifier that is part of the file name for a WMO format file.

[NASA Station Abbreviation] - Same thing but for NASA-Ames files

[BackGround Current Evolution] - This has to be set manually for Vaisala flights depending on the practice at your station. Sndpro can’t determine which is used from the ‘Z’ file . This field is also used when processing T-MAX data. Should be either "Constant" or "Pressure".

[Background current Type] - Same problem as above. This must be set manually to either "1" for ib1 or "2" for ib2. Depending on which is chosen the other value can be added in the main dialog box later if desired.

[Pump Correction Table] - Same problem again. These values must be manually set according to the practice at your station and for a particular flight. Usually this only needs to be done once for a particular station.

[Vaisala Box Temperature] - Usually the ‘box’ temperature used to calculate the ozone partial pressure from the sonde is not included in the ‘Z’ file output. There are two ways to get it. 1) add a second variable to the special sensor handler for temperature (‘Z’ file) or 2) calculate it from the raw telemetry in the ‘S’ file. Either choice can occasionally cause problems so option 0 allows a flight to be read in without any box temperature information.

Entering a flight

Vaisala

After editing the Sndpro.ini file to reflect the practice at your station just open the ‘Z’ file. A ‘S’ file of the same name in the same directory will also be read if this option is selected for the box temperature.

T-MAX

Edit the Sndpro.ini file to select the station you are analyzing as the default. This allows the correct values to be read in for station name, ID, elevation and Lat and Long. Select the file (must have a .dat extension) and Open it from the main menu. A dialog box will appear with places to enter the start time, pump rate and the background current. There is also a button which will display an edit window with the raw telemetry data which will allow you to examine the flight and select those values (just cut and paste your selection). It is also a good idea to examine the data now for obvious errors such as telemetry drop-outs or increasing pressure values. Only ascent data should be used since Sndpro may crash if the pressure data isn’t decreasing smoothly through the flight after the launch time. Any data before the release time is ignored.

Editing the flight / QC

Once the flight data has been entered it should be checked for errors. The data is accessible through the main data dialog form which opens automatically when the flight is first loaded. The station ID, name, altitude and values used to calculate the data can’t be changed directly (you can only change them by re-loading the flight) but most other things can be. The project name, organization, contact person and the comments can be altered directly using the edit boxes along with the date and time of launch. These values are initially set by the defaults in Sndpro.ini and the operator name and comments are read in directly from the Vaisala ‘Z’ file.

To check for clear errors such as pump battery failures, telemetry drop-outs or other problems the first step is to examine the profile data using a plot. To generate a plot just select the menu item under the Window heading. The partial pressure plot is useful for identifying problems in the troposphere or ozone peak region and the mixing ratio plot is better for identifying problems near the top of the flight. The Time-Pressure plot can help identify a faulty aneroid by showing an inconsistent ascent rate through the flight.

If an obvious error is noticed it can be corrected or removed by clicking on the "Edit Flight Data…" button. This opens a notepad editor with the processed flight data in it. Remove bad telemetry points or cut-off a flight early if there was a problem with the sonde by deleting lines in this file. When you are finished just close the editor and save the file if any changes were made. Be sure to add a few comment lines to explain what you did if you decide to change anything.

Whenever the main dialog form looses the input focus (when you click on something else on your screen) all of the changes you have made are accepted into the program and are reflected in any other open windows such as graphs or output formats. This may take a few seconds depending on your computer since Sndpro has to re-calculate selected levels, estimate the tropopause, integrate total ozone and update the other windows etc. If you have a slow computer it may appear to be hung so please wait for a while before giving it the big finger (re-set).

The "Automatic Update" check box can be used to stop SNDPRO from re-calculating the selected levels and normalization factors. The default for this value is checked whenever a raw data file is used as input and unchecked when a X-CSV file is used. This is so that the original values for these fields can be maintained from the X-CSV if desired.

Note: If Sndpro crashed when you click outside the main dialog window there is probably something wrong with the flight data that is making the program attempt an illegal operation. Load the flight again and click the "Edit Flight Data…" button before doing anything else to check that the pressure is smoothly dropping throughout the flight and there are no glitches in the telemetry.

Normalizing

It is a common practice to scale the sonde output to agree with a total column ozone value measured by a ground based spectrometer such as a Brewer measuring at the same time. To do this there must be a total ozone value calculated by the sonde. This requires an estimate of the ozone above the burst height or ‘residual’ ozone. The current version of Sndpro does this by taking the average mixing ratio of the last three significant levels above 17mb and extrapolating to zero pressure. If the sonde doesn’t reach at least 17mb no total ozone is estimated. This is the practice with the Canadian sonde data. Other options could be made available in a later version if there is interest.

Total ozone values from the ground instrument are entered in the LSXXX format with the first two characters indicating the observation type and the last three characters the total ozone in Dobson Units. The instrument type and serial number should also be indicated.

There is some disagreement among data originators over whether routine normalization of sonde flights improves the accuracy of the data or not. This is especially true in regions where the constant mixing ratio assumption may not be valid or where the quality of the ground based measurement is in doubt. However, the ground based total ozone measurement is still a useful diagnostic tool when trying to understand systematic effects in a series of flights.

The X-CSV format allows a total ozone value from a ground based instrument to be recorded without actually normalizing the profile data to it. In this case the normalization factor is just left blank. The check box called "Normalization applied" can be turned off to permit this option. The default (checked)

is to apply the normalization whenever a total ozone measurement is available.

In the other data formats de-selecting this option means the normalization factor and the total ozone value are left unrecorded. In the NASA format the normalization is never applied for consistency with the common convention.

Output formats

These are a few of the common text outputs used for sonde data. To generate them just select the menu item under the ‘Window’ menu heading. This will generate a text window with that particular format which can be saved to disk. A default name will be generated for the file but this can be changed. The text can also be printed if desired.

The text windows or ‘views’ are read only. If you want to change something like a comment or project name do this from the main dialog window.

NASA-Ames

Standard 2160 format with the column headings, units and order following the convention used during the MATCH campaigns to make reading the profiles simpler. The normalization factor is NOT applied.

X-CSV

This is the new standard for the World Ozone Data Centre. Sndpro includes all of the required fields and the optional ones when the data is provided. A detailed description of this format is available from the WOUDC

WMO-Fixed Format

The old punch-card derived standard. This includes only the standard and significant levels in a tight, fixed position format.

Only a sub-set of the data is available in this form. This limitation is one of the motivations for the change to X-CSV

PRO-Format

This format has been used for many years at AES and was a way to display the old WMO-Fixed Format data in a more user friendly manner. It’s good for dropping the data into a spread sheet or just examining it by eye.

Graphs

The graphs can be printed but there is no direct way to save them to a file.

Jonathan Davies

May 1999