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Scientists do not measure an empty hole. They measure how much ozone is in the atmospheric column above each location, how that amount changes across Antarctica and through the season, and at which altitudes the loss occurs. Satellites provide wide-area maps, ground spectrophotometers maintain calibrated long-term records, and balloon-borne ozonesondes supply vertical profiles. The results are commonly expressed in Dobson Units (DU).
What scientists mean by “measuring the ozone hole”
Ozone is spread through the atmosphere, with most of it in the stratosphere, rather than concentrated in a sharply edged sheet. A measurement therefore starts with a defined question: how much ozone is above a point in the atmosphere, or how is ozone distributed with height?
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A total-column measurement adds the ozone from the surface to the top of the atmosphere. Mapping that quantity shows where the column has become unusually depleted and how the affected region expands or contracts. It does not, by itself, reveal the altitude of the loss. A vertical profile records ozone at successive heights, which is why balloon soundings and satellite profiling observations are used alongside column maps.
The phrase “ozone hole” describes a region and season of severe depletion identified from these measurements. It is not a literal cavity through which air or radiation passes.
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Three observing systems answer different parts of the question
| Method | What it measures | Coverage | Sunlight dependence | Main role |
|---|---|---|---|---|
| Dobson or Brewer spectrophotometer | Total ozone above a fixed station | One observing site | Uses sunlight and ultraviolet wavelengths | Long, calibrated ground record and satellite checks |
| Satellite instrument | Total-column ozone; some instruments also retrieve profiles | Regional to near-global swaths | Ultraviolet observations require suitable illumination | Maps the geographic extent and movement of depletion |
| Balloon-borne ozonesonde | Ozone concentration as a function of altitude | A vertical path above the launch site | Can operate during low-sun-angle and dark periods | Resolves where in the atmosphere ozone is being lost |
How Dobson and Brewer instruments measure total ozone
Ultraviolet absorption is the signal
Ozone absorbs some ultraviolet wavelengths much more strongly than others. A ground instrument views sunlight after it has traveled through the atmosphere and compares the intensity at selected wavelengths. The amount of differential absorption indicates how much ozone the light encountered on its way to the detector.
Dobson spectrophotometers
A Dobson instrument uses an internal optical wedge to compare the intensity ratio of two ultraviolet wavelengths. Because the comparison is made between wavelengths affected differently by ozone, the ratio can be converted into the total amount of ozone above the station. The South Pole Dobson record began in 1961, giving researchers a multi-decade reference for Antarctic changes.
Brewer spectrophotometers
A Brewer measures light directly at several ultraviolet wavelengths. Brewers entered the global network in 1982 and provide another established method for total-column observations. Operating both instrument types at stations and comparing their results helps identify instrumental drift or changes in observing conditions.
Calibration and intercomparison
A number from a spectrophotometer is useful only when the instrument’s response is known. Networks characterize instruments, perform regular calibration, and compare observations with other instruments or with satellite measurements. Certification can be carried out directly between instruments or through a satellite-transfer procedure. These intercomparisons let scientists distinguish a real atmospheric change from a change caused by optics, detectors, maintenance, or processing.
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What a Dobson Unit actually represents
A Dobson Unit is a column amount, expressed as the thickness of an equivalent layer of pure ozone brought to reference conditions. It is not the thickness of a physical ozone sheet floating at one altitude.
- 1 DU corresponds to a 0.01 millimetre layer of pure ozone at 0°C and one atmosphere.
- 300 DU would make an equivalent 3 millimetre layer under those reference conditions.
To obtain a total-column value, an instrument’s measured ultraviolet absorption is converted to the amount of ozone above the observing site and reported in DU. A map colored by DU therefore represents the integrated column, not ozone concentration at a particular height.
How satellites map Antarctic ozone
Looking through or down the atmosphere
Satellite instruments observe ultraviolet light as it passes through, or is reflected through, the atmosphere. The measured spectrum is compared with the absorption expected from ozone and other atmospheric constituents. Repeating that retrieval along the satellite’s path produces a broad-area map rather than a single station value.
NASA identifies the Ozone Monitoring Instrument (OMI) on the Aura satellite and the Ozone Mapping and Profiler Suite (OMPS) on NOAA-20, NOAA-21, and Suomi NPP among the instruments used for total-column observations. NASA describes the geometry plainly: “A satellite or aircraft spectrophotometer is aimed straight down to capture the amount of ozone in a vertical column.”
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Total-column products versus profiles
A downward-looking total-column product combines all ozone between the ground and the top of the atmosphere. OMPS also makes side-on observations that can be used to estimate how ozone varies with altitude. Those profile products answer a different question from a total-column map and should not be interpreted as interchangeable.
Why satellites need ground checks
Satellites cover places that cannot host a permanent station, but their retrievals depend on calibration, viewing geometry, algorithms, and instrument health. Long-running Dobson and Brewer observations provide independent reference points. Scientists compare coincident satellite and ground measurements to evaluate bias, detect drift, and keep records from different missions consistent over time.
How balloon-borne ozonesondes reveal the altitude of depletion
The ascent creates a vertical profile
An ozonesonde is carried upward by a weather balloon. As the balloon rises, the instrument records ozone at successive altitudes, producing a detailed profile through the troposphere and stratosphere. The profile can show whether a low total-column value is associated with a pronounced loss in the stratospheric layer or with smaller changes spread across several heights.
Why sondes matter during Antarctic darkness
NOAA Global Monitoring Laboratory notes that polar ozonesonde profiles can be obtained during low sun angles and dark periods, when satellite ozone observations are limited. The sonde does not need sunlight to sample the air while it is ascending, so it fills an important seasonal gap in the observing system.
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What happens when the balloon bursts
A balloon does not always reach the top of the atmosphere. NOAA’s total-column calculation integrates the measured profile up to the burst altitude and then adds a residual estimate for ozone above that height, based on climatological ozone tables. The resulting column is therefore a combination of directly measured ozone and a documented estimate for the unmeasured upper portion. That qualification matters when comparing a sonde-derived total with a satellite or ground-spectrophotometer value.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How scientists combine the measurements
Researchers treat the observing systems as complementary rather than choosing one “best” instrument. A typical analysis follows this sequence:
- Collect station observations. A Dobson or Brewer measures total-column ozone whenever usable sunlight is available, creating a continuous local reference where the station operates.
- Build the satellite field. Ultraviolet satellite observations are processed into total-column values across the Antarctic region. Instruments with profiling capability can provide additional altitude information.
- Launch ozonesondes. Weather balloons sample the vertical distribution, especially during the austral spring period when the depletion is most consequential and satellite illumination can still be restricted.
- Check consistency. Coincident ground, satellite, and sonde results are compared. Differences are investigated through calibration records, viewing conditions, profile integration choices, and the satellite retrieval itself.
- Analyze change. Scientists examine the geographic pattern, the altitude of the loss, and the timing of recovery or further depletion rather than relying on a single reading.
Why the Antarctic calendar changes what can be measured
Ultraviolet spectrophotometers and many satellite techniques depend on sunlight. At the South Pole, the winter brings a prolonged period of darkness, so sunlight-based observations are restricted or unavailable. As the Sun returns, station and satellite measurements become more practical.
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The NOAA South Pole program began Dobson monitoring in 1961 and weekly balloon soundings in 1986. Its description says soundings increase to about three per week during austral spring, September through November. That is a description of the program’s observing pattern, not a guarantee of the operational schedule in every year, including 2026.
This seasonal design explains why a published ozone-hole analysis may combine a long station record, satellite maps during illuminated periods, and balloon profiles obtained when satellites have less useful ultraviolet viewing.
How to read an ozone-hole map without misinterpreting it
- Check the unit. A value in DU is a total-column amount, not a concentration at a stated altitude.
- Check the product type. A total-column map and a vertical profile cannot answer the same question.
- Check the date and season. Antarctic ozone changes rapidly through spring and then evolves as sunlight, circulation, and chemistry change.
- Check the observing method. A station value represents one location; a satellite pixel represents an area; a sonde samples a narrow vertical path.
- Check the processing notes. Sonde columns may include a climatological residual above balloon burst altitude, while satellite values depend on retrieval algorithms and calibration.
A map can show where the column is low without proving exactly where in the atmosphere the loss occurred. For that, the map must be interpreted with profile measurements.
What the instruments can—and cannot—establish
Together, the systems can establish the amount of ozone above locations, the spatial pattern of depletion, and the altitude range in which ozone changes are concentrated. Their agreement across independent methods strengthens confidence that a mapped feature is atmospheric rather than an instrument artifact.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchNo single observation supplies every piece of information. A ground spectrophotometer has a precise location but limited spatial coverage. A satellite sees broad areas but faces illumination, calibration, and retrieval constraints. A sonde gives fine vertical detail but follows one balloon path and may require an estimate above burst altitude.
Season-specific figures such as the year’s minimum ozone, maximum affected area, duration, or recovery status require a dated NASA or NOAA release for that season. Measurement methods explain how those values are obtained; they do not make a 2026 result permanent or interchangeable with an earlier year.
The central idea
Scientists measure the ozone hole by combining column amounts and altitude-resolved observations. Dobson and Brewer instruments anchor long-term total-ozone records at stations. Satellites turn ultraviolet observations into regional and global maps, with some instruments adding profile information. Balloon ozonesondes trace ozone through the vertical atmosphere, including periods when low sunlight limits satellite observations. Dobson Units provide the common language for the total column, while calibration and cross-checks keep measurements comparable over decades.
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