Volcano FITS Notes

Observation site

In FITS, the observation site, the feature at the volcano where the observations are collected, is referred to as the siteID. This is unique to a location. SiteIDs can be found using GeoNet’s FITS data service’s site query.

For volcano observations, the first part of the siteID is a two-letter upper case code which represents the volcano where the site is situated. The second part of the siteID is a three-digit number, with leading zeros.

Two-letter volcano codes

Example of a siteID

At the outlet of the crater lake at Ruapehu, GeoNet makes observations of lake temperature and lake water level, and collects samples of lake water for laboratory chemical analyses. The siteID for this site is RU001.

SiteID representing the whole volcano

To indicate a volcano as a whole, and not a specific feature at a volcano, the numeric part of the siteID is 000. For example, when dealing with volcanic gases from Whakaari/White Island, which can represent the aggregated output from all vents and features at the volcano, the siteID is WI000.

SiteIDs for groups of sites collecting the same kind of data

For convenience, sites at a particular volcano that are used to collect the same kind of observation are assigned similar siteIDs, with the numeric part of the siteID drawn from a consecutive series of numbers. For example, there are 22 sites on the shore of Lake Taupō used for periodic measurements of vertical ground deformation, and their siteIDs range from TP001 to TP022. At springs, pools and streams at Whakaari/White Island, where water samples are collected for laboratory chemical analysis, the siteIDs range from WI220 to WI227. At Tongariro, springs, pools and stream siteIDs range from TO050 to TO063.

Managing small changes to observation sites

There are sometimes small changes to features at volcanoes where observation data are collected that are stored in FITS. These changes are often in the shape or structure of a feature and can require a small change in the data collection location, typically no more than a few metres. This situation is not uncommon at springs or pools in changing volcanic environments, and these feature changes can require a slightly different location to be used to collect water samples; this needs to be reflected in the siteID as there can be related differences in chemical composition of the water samples or feature temperatures. As the location difference is usually very small, rather than assigning a new siteID, a hyphen and a one-digit number are added as a suffix. This is similar in intention to the location code GeoNet uses to name seismo-acoustic data streams. An example will clarify this.

At Whakaari/White Island, there was a spring on the crater floor called Black Pot. Water samples were first collected in 1995 and observations from these samples are stored in FITS. Since 1995 there have been a series of small changes in that area and the siteID has been adjusted accordingly.

Observation Type

In FITS, the observation type, the type of data that are stored in FITS, is referred to as the typeID. This is unique to an observation type. TypeIDs can be found using GeoNet’s FITS data service’s type query.

Observations having the same typeID can be collected at multiple sites and observations having different typeIDs can be collected at one site.

The typeID is given by a character string. The length of the string is as short as possible to provide a unique and meaningful code/abbreviation for the type of observations collected.

Examples of typeIDs

Analyte concentrations in a water sample

The typeID for the concentration of an analyte in water collected at springs, pools and streams is made up of the chemical formula of the analyte followed by -w to indicate that the concentration was measured in a water sample.

For example, the typeID Mg-w represents the concentration of magnesium. In some cases, the way samples are analysed requires an extra component to the typeID. For example, phosphate concentration is measured as phosphorus, so the typeID is PO4-P-w, with PO4 being phosphate and P being phosphorus.

The typeID for isotopes of ¹⁸O (oxygen-18) and ²H (deuterium) are measured relative to their respective stable isotopes. This is referred to as delta-O-18 and delta-H-2. The typeIDs are therefore d18O-w and d2H-w, respectively.

Temperature and height

Temperature and height are common types of observations that are made at several kinds of volcanic features and stored in FITS. Temperature has a typeID of t. Height is used to refer to the height of a point on land relative to some reference and commonly also to refer to water level. In both cases the typeID is z.

Gas discharge rate (gas flux)

Gas discharge rate, commonly referred to as gas flux, is a measure of the volume of gas being discharged in a unit of time. Gas discharge can be measured as it leaves the ground, or in the air above the volcano, as an aggregated output from all vents and features at a volcano.

Gas discharge measurements are commonly applied to three gases, sulphur dioxide (SO₂), carbon dioxide (CO₂), and hydrogen sulphide (H₂S). When measured as it discharges from the ground, the typeIDs are SO2-flux-e, CO2-flux-e, and H2S-flux-e, respectively. When measured in the air, the typeIDs are SO2-flux-a, CO2-flux-a, and H2S-flux-a, respectively.

Weather related

Observations of weather and weather related phenomena are often made at volcanoes as they are relevant for interpreting the temperature of features and the wind velocity is used for calculating gas discharge rate.

Crater lake and hot springs related

GeoNet monitors Raoul Island, Ruapehu, White Island and Waimangu (Rotorua) crater lakes. The following measurements are recorded at crater lakes. Not all observations are available from each lake.

Data collection method

In FITS, the data collection method, the way the data that are stored in FITS are collected, analysed, or processed, is referred to as the methodID. This is unique to a data collection method. The methodID is given by a short character string, an abbreviation of the name of the method, with the length of the string just long enough to provide a unique and meaningful code. MethodIDs can be found using GeoNet’s FITS data service’s method query.

With volcano data, it is common for several methods to be used to collect observations having the same typeID. Some of this relates to the era when observations where collected, for example, old temperature observations were almost always collected with a mercury thermometer, and more recent observations might be made with a thermocouple, or some other device.

In other cases, the method used to collect an observation depends on the volcanic conditions and/or access limitations imposed by the volcanic environment at the time. For example, water level in a volcanic lake might be measured manually relative to a staff gauge when site access is possible, or by using repeated photographs to compare water level against features of known height when access is not possible. In other situations water level might be determined using a special water level sensor recording onto a data logger. A single site could therefore have water level observations using three or more different methodIDs.

Examples of methodIDs

Collecting temperature observations

Laboratory Analysis

Water samples collected from springs, pools and streams are analysed in a laboratory and the concentration of various analytes is returned. Typically several different analysis techniques and equipment are used to provide the range of analyte concentrations required for volcano monitoring. For a given analyte, the specific technique and equipment used is not recorded in FITS; it will change through time as the capability of different techniques and equipment used in the laboratory develops. All chemical analysis of water samples are given the same methodID, lab, for a geothermal water chemistry laboratory.

Gas discharge rate (gas flux)

Gas discharge rate, commonly referred to as gas flux, is a measure of the volume of gas being discharged in a unit of time. Some gases require specific measurement techniques and others are often measured using more than one technique.

Sulphur dioxide (SO₂) can be measured flying in an aircraft near a volcano. In that case are two methodIDs, cosp, when a COSPEC instrument is used to fly beneath a volcanic plume, and cont, for contouring, when the aircraft flies through the plume at different heights and a pump inside the aircraft sucks in gases for analysis. A Flyspec, methodID flsp, can be used in the same way as a COSPEC.

Sulphur dioxide can also be measured using ground-based mini-DOAS instruments. In this case there are two methodIDs, mdoas-ah, when the plume is observed by only one instrument and the height of the plume has to be assumed, and mdoas-ch, when the plume is observed by more than one instrument and the plume height can be calculated.

Carbon dioxide (CO₂), and hydrogen sulphide (H₂S) discharge rates can only be determined using the contouring technique, so both always have a methodID of cont.

Data retrieval examples using the API

Specify typeID and siteID

TypeID and site ID are the minimum we can specify to retrieve observation data from FITS; what kind of data and from where.

Temperature (typeID t) data collected at the crater lake at Whakaari/White Island volcano (siteID WI201) using GeoNet’s FITS API.

https://fits.geonet.org.nz/observation?typeID=t&siteID=WI201

The issue with the results returned by this query is that we get data returned that have been collected using two different methods, and we cannot distinguish one from the other. In some cases this does not matter, but in many cases it does. To fix this we need to include the methodID in our query.

Specify typeID, methodID, and siteID

Temperature (typeID t) data collected using an infrared thermometer (methodID therminfra) at the crater lake at Whakaari/White Island volcano (siteID WI201) using GeoNet’s FITS API.

https://fits.geonet.org.nz/observation?typeID=t&methodID=therminfra&siteID=WI201