Data Quality Assessment Tools
There are several tools available to IRIS data users to allow a view of the quality of data flowing into the IRIS Data Management Center. These tools measure signal RMS and Mean, Data availability, number of gaps and overlaps, timing quality, data latency, noise statistics, STA/LTA ratios and probability density functions of power spectral density estimates (called PDF plots).
Since Summer 2003, data flowing through the IRIS DMC's near-real time data collection systems (BUD and USArray) have been analyzed by an automated software package known as the Quality Analysis Control Kit (QUACK). The quality parameters measured by QUACK are stored in a relational database. Internet users can explore and view measurement parameters made by QUACK via a user interface. Additionally, QUACK includes an e-mail reporting mechanism, targeted at network operators or those looking for bulk, regularly reported quality metrics on realtime data streams.
Explore the QUACK!
From the QUACK homepage, there are several options to put together charts, plots, and images that express data quality metrics. Feel free to explore the tools and see what's available. For GSN-specific users, a good QUACK practice is to first click on the "Filter Results" link . This directs the QUACK resources to only be applied to stations of interest (virtual network, data collection system, and/or active channels). By selecting the _GSN virtual network, the response time of the QUACK will improve and you will only see the information related to GSN stations.
Once filters are applied, a good starting point is the "Explore Data" link on the QUACK page. This interface allows access to all the metrics on a station-by-station, channel-by-channel basis for all the data in the BUD and USArray near-real time systems. Clicking on network, station, location codes and channels allows a look at the individual channel measurements available. Each "measurement" link opens access to various report forms (images, time histories, etc) pertinent to the metric. Drilling down on PDF plots allows a look at multi-year, annual, monthly, weekly, and daily PDF plots or you can even generate your own custom date range. This tool will even allow a look at what part of the spectral estimates were made during which part of the day (excellent for analyzing diurnal noise variations). This is accomplished by bringing up a daily PDF plot and clicking on the "explore time of day dependencies..." link.
If you're looking for more than single channel metrics, you can explore the "Reports" page which allows you to customize reports of these metrics for multiple stations and channels. The QUACK Report Maker allows you to select combinations of networks (including virtual networks), stations, location codes and channels and any combination of the metrics available (wild card selections are enabled) for a preset or custom date range.
More information on the QUACK can be found on the IRIS DMS Electronic Newsletter (Volume VIII Number 1)
A Quick QUACK Tutorial: Exploring Seismograms and Data Quality
To explore your favorite station, go to: http://www.iris.edu/servlet/quackquery/budFileSelector.do
Produce a Helicorder Plot
Pick a network, station, channel, e.g. for Chile select C, GO05 ("gee oh zero five"), -- (blank blank), BHZ
Under Measurements -> Select a day e.g. 2012.027
Under Display Data -> Select "Webicorder . . . "
The result is a 24 hour velocity seismogram, so high frequencies are emphasized.
Note the Chile network stations are GO0x ("gee oh zero _ _", not "gee zero zero _ _") and the location identifier is "blank blank".
Examine the Station's Ambient Noise Levels
Under Measurements -> Select NEIC PDF Plot
Under Display Data -> Select year & month of interest
A new page appears with daily or monthly PDF's.
Click Here to explore time of day dependencies and then click on the PDF to determine which time intervals contributed to the signal power at that point.
Various clicks on the BUD Explorer "quackquery" page will show you other interesting characteristics of the daily, monthly and yearly parameters, e.g.:
All of these are routinely pre-processed and stored for all data that are available from the DMC in real time.
Query Available Data
If you want to know what other channels are recorded at a given station, go to: http://www.iris.edu/SeismiQuery/channel.htm
Fill in the Network Code and/or Station Name.
Click "View Results" to get a list of the designation and description of the recorded channels.
Access Waveform Data
The web service "time series builder" provides an easy way to explore and display individual waveforms and download data segments from the DMC: http://www.iris.edu/ws/builder/timeseries/
For a local earthquake recorded at GO05, the default parameters give:
Some tweaking of the filter and display options for the same event gives:
For a teleseismic event recorded at GO05:
The selected data segments can be downloaded with the "Output" button on the lower right.
The IRIS DMS is currently working on the next generation of Quality Assessment Tools that will expand the capabilities of the QUACK with more tools and will allow application of the tools to the complete data archive at the IRIS DMC rather than just to those channels received in near-real time. As those tools come online, this page will be updated.