Difference between revisions of "Help:Using the Concentration Anomaly Tool"

From Earth Science Information Partners (ESIP)
Line 1: Line 1:
- Explain time window width setting.
+
A useful measure of the "normal" concentration is the 84th percentile (+1 sigma) for a given station. A concentration anomaly is a deviation from the normal. This tool permits the calculation of concentration anomalies. In the illustration below, a time windows of +/- 15 days (one month window) was chosen. This period is longer than a typical exceptional event, but it is sufficiently short to preserve seasonality. In order to establish the normal values the concentrations can be averaged over multiple years for the given time window measured in Julian days, i.e. days between 160 and 190. Hence, a particular sample is considered anomolously high (deviates from the normal) if its value are substantially higher than the 84th percentile of the multi-year measurements for that "month" of the year.  
A useful measure of the "normal" concentration is the 84th percentile (+1 sigma) for a given station. A concentration anomaly is a deviation from the normal. This tool permits the calculation of concentration anomalies. In the illustration below, a time windows of +/- 15 days (one month window) was chosen. This period is longer than a typical exceptional event, but it is sufficiently short to preserve seasonality. In order to establish the normal values the concentrations can be averaged over multiple years for the given time window measured in Julian days, i.e. days between 160 and 190. Hence, a particular sample is considered anomolously high (deviates from the normal) if its value are substantially higher than the 84th percentile of the multi-year measurements for that "month" of the year. See [[Help:Using the Concentration Anomaly Tool]] to learn how to change these parameters.
 
  
 
[[Image:070524_FRMpm25_TimeSeries_280870001.png|800px]]<br>
 
[[Image:070524_FRMpm25_TimeSeries_280870001.png|800px]]<br>
Line 14: Line 13:
 
The anomaly calculation parameters of the Concentration Anomaly Tool can also be adjusted, changing: (1) the percentile that is defined as "normal" and (2) the calculation to find the  difference from normal.  
 
The anomaly calculation parameters of the Concentration Anomaly Tool can also be adjusted, changing: (1) the percentile that is defined as "normal" and (2) the calculation to find the  difference from normal.  
  
 +
The tool has three layers that can be viewed and changed: Time Instance, Time Range and computed.
 +
 +
=== Time Parameters ===
 +
To change the event day:
 +
# Select Time Instance Layer and change the date, click go.
 +
 +
To change the Time Range:
 +
# In the time view, click the magnify glass
 +
# Change time_min and time_max. Click Ok and then in the viewer click the red "Go" Button. The Time view will refresh with the new range.
 +
# Note: This changes the window that the anomaly calculation uses to average over.
 +
 +
To change the Time Window:
 +
# Click Service Program
 +
# Select GetCoverage data_range
 +
# In the Time box, change Julian Day Window - days before/days after.
 +
# Save and update browser.
 +
 +
=== Anomaly Calculation Parameters ===
 +
 +
To Change the Percentile:
 +
# Click Service Program
 +
# Click Time Aggregate for the Time Range layer.
 +
## To change the function click drop down box that says 'Percentile' and select desired function (e.g. Median, Avg, Sum)
 +
## To change percentile edit the text box below.
 +
 +
To Change the Anomaly Calculation:
 +
# Click Service Program
 +
# Click Evaluate Exp on the Computed Layer and modify the expression
  
  
=== Normal and Exceptional Pattern Analysis Tool ===
 
The pattern of air air pollution pattern varies in space, time and also depends on the pollutants. In case of PM, it also depends on the species in the PM chemical mix. The sulfate pattern, for example, is very different from nitrate, organics or dust. An event being exceptional, requires the it deviates from the "normal", but what is normal?
 
  
 
[[Image:CATT Map ServiceProgram.png|400px]]
 
[[Image:CATT Map ServiceProgram.png|400px]]

Revision as of 11:56, June 2, 2008

A useful measure of the "normal" concentration is the 84th percentile (+1 sigma) for a given station. A concentration anomaly is a deviation from the normal. This tool permits the calculation of concentration anomalies. In the illustration below, a time windows of +/- 15 days (one month window) was chosen. This period is longer than a typical exceptional event, but it is sufficiently short to preserve seasonality. In order to establish the normal values the concentrations can be averaged over multiple years for the given time window measured in Julian days, i.e. days between 160 and 190. Hence, a particular sample is considered anomolously high (deviates from the normal) if its value are substantially higher than the 84th percentile of the multi-year measurements for that "month" of the year.

070524 FRMpm25 TimeSeries 280870001.png

The time parameters of the Concentration Anomaly Tool can be adjusted, changing: (1) the event day, (2) time window and (3) the time range that the time window is averaged over.

There is also need for flexibility in defining the 'normal' when calculating the deviation above normal. For example in figures below, the excess concentration is plotted based on 'normal' defined as the 50th, 84th (+ sigma) and 95th percentile of the distribution. Clearly, on a given day, the excess above the 95th percentile is much smaller than excess above the 50th percentile.

PM25 DiffAboveNorm50Perc.png PM25 DiffAboveNorm84Perc.png PM25 DiffAboveNorm95Perc.png

The anomaly calculation parameters of the Concentration Anomaly Tool can also be adjusted, changing: (1) the percentile that is defined as "normal" and (2) the calculation to find the difference from normal.

The tool has three layers that can be viewed and changed: Time Instance, Time Range and computed.

Time Parameters

To change the event day:

  1. Select Time Instance Layer and change the date, click go.

To change the Time Range:

  1. In the time view, click the magnify glass
  2. Change time_min and time_max. Click Ok and then in the viewer click the red "Go" Button. The Time view will refresh with the new range.
  3. Note: This changes the window that the anomaly calculation uses to average over.

To change the Time Window:

  1. Click Service Program
  2. Select GetCoverage data_range
  3. In the Time box, change Julian Day Window - days before/days after.
  4. Save and update browser.

Anomaly Calculation Parameters

To Change the Percentile:

  1. Click Service Program
  2. Click Time Aggregate for the Time Range layer.
    1. To change the function click drop down box that says 'Percentile' and select desired function (e.g. Median, Avg, Sum)
    2. To change percentile edit the text box below.

To Change the Anomaly Calculation:

  1. Click Service Program
  2. Click Evaluate Exp on the Computed Layer and modify the expression


CATT Map ServiceProgram.png