Resample Type:
- None - no resampling. This is the default option for time series scalar data.
- Average - the mean value within resample period (fixed-window averaging without overlap). This is also known as a 'box-car' or ensemble average. Only available with the clean data product option.
- Min/Max - only available for some plotting data products - the most extreme minimum and maximum values within resample period. QAQC flags are taken as the worse case flag from the data points found within the resample interval, even if those points are not the maximum or minimum. (At this time, the time stamps of the minimum/maximum values are not provided, only the bin-centered time stamp. This is why this option is not currently offered for time series scalar data, but it will offered again once the full time-stamps are provided.)
- Min/Max+Avg - only available for some plotting data products - the combination of the min/max and average as described above. QAQC flags are the same as the min/max case, however, the average is always calculated on clean data and will be NaN if there is less than 70% data available after cleaning. This is the default option for time series scalar plots, other plots, such as the BHT, AGO, profile or staircase plots will have different options and defaults.
Resample Period:
Visible when an actionable resample type is selected, immediately to the right of the resample type. Current periods offered:
- 1 Minute
- 10 Minute
- 15 Minute
- 1 Hour
- 1 Day
- Automatic (plots only)
When resampling is selected:
- The timestamps in the data series correspond to the centre of each resampling interval. (Data downloaded prior to 13 Feb 2013: timestamps were at beginning of interval). The resample interval always begins and ends at an integer multiple of the resample period, so minutes on the minute, hours on the hour, days on the day, etc.
- If the date/time range on the search has limits that are within a resampling interval, the date/time endpoints are extended to include the entire resampling interval. For example, when daily resampling is selected from 03:00:00.000 on Monday to 20:00:00.000 on Thursday, the date range is extended to 00:00:00.000 on Monday to 23:59.59.999 on Thursday.
- Note that tides are not filtered out in resampled products.
- No anti-alias filtering is done. This is why only averaging and min/max are offered at this time. Box-car / ensemble averaging is an easily understood and ubiquitous process that is actually a partially effective low-pass anti-alias filter. For more information, see this page on data reduction and time-averaging.
- All averages are calculated by adding all individual samples and then divide by the total number of samples. (Data downloaded before 13 Feb 2013: hourly and daily averages were weighted over 15-minute periods, that is, the average of each 15-minute period was calculated individually, and the hourly and daily averages were calculated from the 15-minute averages.)
- If the clean data product option is selected: resampled values will not be provided if less than a certain percentage of the expected samples per resampling interval are present (either because of data gaps or low data quality determined by Quality Assurance Quality Control). The current default for the data completeness percentage is 70%. It was 80% from March 21, 2013 to to June 6, 2013. Prior to March 21, 2012, no data completeness or quality assurance was tested for. Future improvements will allow users to modify the data completeness threshold. The data completeness check is not done for the raw data product option.
- (plots only) Automatic resampling chooses the most appropriate resample period for min/max+avg resampling, such that the amount of data returned is adequate for plotting.
More options will be available in the future as we work to improve the data products. Feedback is welcomed and encouraged. For custom resampling, users can develop their own matlab code in CodeRunner in the ONC computing environment (users can access all production data and code). See CodeRunner Help for more details.
File-name mode field
The resample type and period are added to the file-name when resampling is selected. Examples: 'avg1hour', 'MinMax10minute'.