Figure 1. COHOWeb System Diagram
A full featured technical paper about WWW-based data systems presented to the Science Information Systems Interoperability Conference SISIC'95 is available.
A control panel comprising four graphic buttons are present near the bottom of every "page". The control panel, in conjunction with the "back" button on WWW browsers, allow the user to navigate the COHOWeb system.
Figure 1. COHOWeb System Diagram
The e-mail address is used as an unique identifier to track a user's activity within the COHOWeb system and for staging data in directories corresponding to your username for retrieval. Your e-mail address is used for accounting purposes only and will not be published nor distributed.
To use the COHOWeb Data Selector, follow the steps below:
For information on the spacecraft and data, please see the COHOWeb Data document.
The COHOWeb Data Explorer is dynamically generated and customized for the spacecraft selected in the COHOWeb Data Selector, and therefore will appear to be different for each spacecraft.
With the COHOWeb Data Explorer, the user selects an activity, enters start and stop dates, and picks variables to plot or retrieve. Options are also available for advanced plotting features, converting data to various formats, or downloading or listing data.
To use the COHOWeb Data Explorer, follow the steps below:
Enter start and stop dates (use yymmdd or yyddd format)
The start and stop dates indicate the time period of interest. The dates can be entered in the following date formats:
YYMMDD
YYDDD
For example, January 1, 1992 equals 920101 in YYMMDD format and 92001 in YYDDD format. The availability of the data differs among the spacecraft data sets and the valid date range is displayed alongside the start/stop date fields on the Data Explorer form in the YYMMDD format.
The data is stored as hourly averaged values (24 records per day), which is the default resolution to access. The user may also request daily averaged values to compute the average over every 24-hours of data into a single value. This is useful for trend analysis of large periods of time. Daily resolution is only available in plots and ASCII listings.
Basic Plotting
Basic Retrieving
Advanced Plotting
Please see the Advanced Plotting document for more information about advanced plotting features.
The engine of the plotting software is a product from Research Systems Inc. called the Interactive Data Language (IDL). IDL is run in batch mode from which plots are created from the user's selections and written to a GIF file as output. Further information on IDL is available from RSI's Home Page.
The basic plotting options will generate a 640x480 image of the selected options as an inline GIF and the advanced options allow many other features to customize the plots.
Note that by selecting daily resolution, the hourly data will be averaged for each day. Further averaging and smoothing can be done using the NSUM and SMOOTH options from the advanced plotting options.
Much of the plot formatting is done automatically. For example, the axis labeling is determined "optimally" for what is determined as most appropriate. The x-axis tick marks are labeled as time (HH:MM) if the selected time period is less than 48 hours, day of month (DD) if the period is less than two months, month/day (MM/DD) if the period is less less than two years, and month/year (MM/YY) for longer periods.
The time and date are stored in each record as a CDF_EPOCH data type variable, which is a 8-byte double precision floating point value measured in milliseconds since the epoch. This variable is included automatically in all listings and retrieved data files. It will be displayed in the format dd-mmm-yyyy hh:mm where
dd is the day of the month, 1-31,
mmm is the month, Jan, Feb, Mar, ..., Dec,
yyyy is the year, AD,
hh is the hour, 0-23, and
mm is the minute, 0-59.
If the download option is chosen, the user has the additional option of converting the data to one of the formats listed below. The binary formats include the machine-independent NSSDC Common Data Format (CDF). Further information on CDF is available from the CDF Home Page with the URL http://nssdc.gsfc.nasa.gov/cdf/cdf_home.html.
Note that daily resolution values are displayed in listings and plots for browsing long time periods, but not in generated CDF or binary files. All downloaded CDF and raw binary files will be in hourly resolution, which are intended for further analysis.
The following data formats are available for when retrieving data.
The ASCII listing for downloading is more compact than the listing to terminal because it excludes any headers or labels and is more appropriate for large listings. Note that the ASCII listing formats the data values to strings, so some rounding may be involved for floating point numbers. Therefore, anyone concerned with maintaining the integrity and precision of the original data should obtain a CDF or binary data file.
The requested subsetted data files for downloading are created on the NSSDC anonymous ftp site and located in a subdirectory named with the username who requested the data. For example, if the e-mail address was entered as mathews@nssdc.gsfc.nasa.gov then all data for this user will be located in the directory /pub/cohoweb/mathews on our anonymous ftp server. Data can either be transferred one at a time by clicking on the hyperlinks as they are shown or all at once by FTP'ing to nssdc.gsfc.nasa.gov and getting all the files from the user's directory. All files are uniquely named (with spacecraft code followed by process ID; e.g., "he1_8402.cdf") so that no files will be overwritten. The data files will be removed after 48 hours, so users must copy the files to their machine within that time.
Further enhancements to the COHOWeb system will be primarily driven by user requests.
For information on COHO data, please see the COHOWeb Data document.
Question 1: What is the difference between OMNI data on OMNIWeb and OMNI_M data under COHOWeb?
Answer 1: The OMNI_M data set in COHOWeb is a special version of the OMNI near-Earth data set, with the same parameter set, coordinate systems, and formats, included to facilitate multi-point heliospheric analyses. OMNI_M is a subset (only 10 variables) of the OMNI data (44 variables) available via OMNIWeb and converted to correspond with the other COHO data.
V0.9 28-Feb-95 GJM - COHOWeb Version 0.9 comes on-line with retrieval and
limited browsing for a small subset of COHO data.
V0.91 21-Apr-95 SST - Graphical map of the COHOWeb created.
V1.0 27-Apr-95 SST - Help document created.
V1.1 2-May-95 GJM - Added plotting/retrieval and other resources sections.
