All of the questions below are linked to descriptive answers in this chapter of the Giovanni Online Users Manual regarding the Giovanni TOMS instance. Click the question of interest.
What does TOMS stand for? How many TOMS missions were there?
TOMS stands for Total Ozone Mapping Spectrometer. There were four TOMS missions; the first mission was on the Nimbus-7 satellite, and this instrument collected data from Nov 1978 to May 1993. The second mission was on the Russian Meteor-3 satellite, which collected data from Aug 1991 to Dec 1994. On the third mission, TOMS was the only instrument on an Earth Probe (EP) satellite. The EP-TOMS mission began in July 1996 and lasted until the end of 2006.
The fourth TOMS mission was on the Japanese ADEOS (Midori) satellite, launched in August 1996 and which operated to June 1997. Giovanni TOMS does not have data from the ADEOS mission.
Is data available in the Giovanni TOMS instance from all of these missions?
Data is available from each of the three TOMS missions in the Giovanni TOMS instance.
What version of the data is available in the Giovanni TOMS instance? Is this version the same for all of the TOMS missions?
The TOMS data version currently in Giovanni is Version 8. All three of the missons have this same version of the data.
What TOMS data types are available?
The TOMS data types in Giovanni are all Level 3 geophysical products. The TOMS instrument actually measures backscattered ultraviolet radiance from the atmosphere at 6 wavelengths, four of which are sensitive to ozone concentration, and the other two are used for surface reflectivity information, an input needed in the ozone retrieval algorithm.
What data parameters are available in the Giovanni TOMS instance? What is the spatial resolution of the data?
The data parameters available in the Giovanni TOMS instance are listed below. Each data parameter is linked to a short description in the Data Parameter Appendix.
The data areat 1 degree latitude x1.25 degree longitude resolution.
What projections of the data are available in this instance?
Four data projections are available in the current Giovanni instance; Cylindrical Equidistant, which is the default projection; North Polar Stereo and South Polar Stereo; and Robinson. Note that the data for area maps and animations will always be plotted in the default projection first. The other projections can be selected in the "Submit Refinements" step (see the question on plotting preferences below).
What are the current data analysis and visualization (output) capabilities in Giovanni TOMS?
The Giovanni TOMS instance provides the following analysis and visualization options:
How is the spatial area of interest selected in Giovanni TOMS?
The spatial area of interest can be selected by either of the two methods described below
Java applet map: The Java applet map can be utilized to "click and drag" a selection box to designate the spatial area of interest.
Geographic coordinates: The geographic coordinates of the corners of the spatial area box can be input individually. This method can be used if Java is not enabled. Note that decimal and not degree (seconds and minutes) coordinates must be entered.
How is the time period of interest selected in Giovanni TOMS?
The starting date (year/month/day), and the ending date (year/month/day) for the analysis are selected using the calendrical menus on the Giovanni interface page.
Error messages will be generated if the submitted selections for year, month, and day do not correspond to the data set time range, or if the end month or end day precede the start month or start day.
Are there any limits on the time-period or spatial area that can be selected?
As noted above, the time-period must correspond to a time-period during one of the missions. If the start date or end date is not in the time range of the missions, an error will be generated and data processing will not be possible. This criterion applies to multi-mission time series as well.
There are no spatial area constraints. Note: If a region in the Southern Hemisphere is selected and the "North Polar Stereo" option is chosen by mistake, the system will revert to the original interface so that correct selections can be entered.
What are the plotting preference options for this instance?
The plotting preference options are described in the Plot Preferences chapter of the Giovanni Online Users Manual.
After the initial output has been generated, the temporal and spatial ranges (constraints) and plotting preferences can be changed, and a new output generated, using the "Submit Refinements" button. For the Giovanni TOMS instance, this is when the North or South Polar Projections can be selected.
I would like to make a time-series using data from all of these missions together. Is that possible?
At this time, this multi-mission time-series capability is not provided in Giovanni.
What do the statistics mean in the time-series statistics output?
The statistics that are provided with the time-series output are Grid Cell Count, Standard Deviation, Maximum, and Minimum. Grid Cell Count indicates the number of grid cells used from the selected region to generate the mean value shown in the time-series. Standard Deviation is a measure of the variability in the data. Maximum indicates the maximum value within the selected plot area for each time step (a day in this instance), and Minimum indicates the minimum value within the selected plot area for each time step. Further detail on these statistical quantities can be found in the documention of the Time-Series Statistics operation.
I want to make an animation of the ozone hole over Antarctica. How do I do that?
To make an animation of the ozone hole over Antarctica, first select the entire continent of Antarctica using the spatial selection map or geographic coordinates. This means choosing an area that spans the full longitude range. The northern latitude limit should be about 50° S. Then choose a time period when the ozone hole occurs, generally beginning in August and ending in November, and select "Animation" as the visualization preference. After the initial ouput is generated in Cylindrical Equidistant projection, select the "South Polar Stereo" projection option, and then click the "Submit Refinements" button. When the output is generated, run the animation.
I think I read that the ozone hole wasn't really discovered by TOMS. How was it discovered?
Yes, that is true. Actually, when the low ozone levels over Antarctica were initially detected by Nimbus-7 TOMS, the observations were flagged as bad data because they were lower than threshold values that had been established for data processing. It was only after the publication of ozone depletion observations made by British scientists at the Halley Bay base that the TOMS mission scientistsdetermined that decreased ozone concentrations were being detected by TOMS above Antarctica in the austral spring. The data processing was adjusted, so that soon after the publication of the paper, dramatic TOMS images showing the ozone hole were released.