This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 640276.
G2.30 Metrologically incomplete uncertainty quantification for Pandora ozone measurements
Submitted by Anna Mikalsen on 12 June, 2017 - 10:55
Gap abstract:
Pandora is a relatively new UV-VIS instrument for measuring total ozone and also ozone profiles in a similar way as MAX-DOAS instruments. So far only a few studies exist which describe measurement uncertainties or measurement validation. As a relatively inexpensive and automated instrument, there is a strong potential that a network of Pandora instruments could have a substantial role in the satellite validation in the future. A metrologically rigorous uncertainty quantification for the Pandora instrument is therefore needed.
Part I Gap description
Primary gap type:
- Knowledge of uncertainty budget and calibration
Secondary gap type:
- Governance (missing documentation, cooperation etc.)
ECVs impacted:
- Ozone
Non-satellite instrument techniques involved:
- Pandora
There are similarities in filling this gap and G2.31 is related to MAX-DOAS instruments even though there are no critical dependencies.
Detailed description:
Pandora is a relatively new UV-VIS instrument for measuring total ozone and also ozone profiles in a similar way as MAX-DOAS instruments. The instrument is relatively small, inexpensive and automatic. The number of Pandora instruments has been growing during recent years and therefore it is possible that a network of Pandoras could have stronger role in satellite validation in the future. For example, the European Space Agency has recently supported the development of Pandora network called Pandonia.
However, so far only a few studies exist which describe measurement uncertainties or measurement validation (see e.g. Herman et al. 2015, Tzortziou et al, 2012). This yields low confidence that the measurement uncertainties are currently either fully documented or rigorously quantified. For example, systematic uncertainty in Pandora direct-sun measurements are limited by temperature effects not corrected in current operational procedures. The neglect of temperature effects (related to the ozone spectroscopy in the Huggins bands) leads to seasonally dependent systematic biases and synoptic scale biases, of various amplitudes depending on the latitude of the site. This gap is partially addressed within GAIA-CLIM.
Operational space missions or space instruments impacted:
- Copernicus Sentinel 4/5
- MetOp
- MetOp-SG
- Polar orbiters
- Geostationary satellites
- UV/VIS nadir
- Passive sensors
Validation aspects addressed:
- Geophysical product (Level 2 product)
- Gridded product (Level 3)
- Assimilated product (Level 4)
- Time series and trends
Gap status after GAIA-CLIM:
- After GAIA-CLIM this gap remains unaddressed
A literature review has been initiated on the uncertainties related to total ozone retrievals using the Pandora instrument. Based on this and additional information obtained during the CINDI-2 campaign, an analysis of selected types of uncertainties is currently being completed. We expect, in particular, that the outcomes of the CINDI-2 campaign held in September 2016 will provide additional input for this gap. Several Pandora instruments as well as MAX-DOAS instruments have participated in the campaign. Exercises and studies performed during this campaign will provide the community with relevant datasets and information about how to proceed most effectively.
Part II Benefits to resolution and risks to non-resolution
| Identified benefit | User category/Application area benefitted | Probability of benefit being realised | Impacts |
|---|---|---|---|
Understanding of uncertainties related to Pandora instrument. In particular, understanding of systematic errors would be beneficial. |
|
| Improved validation possibilities by using a relatively inexpensive and (quasi-)autonomous instrument. |
| Identified risk | User category/Application area at risk | Probability of risk being realised | Impacts |
|---|---|---|---|
Potential systematic errors may limit satellite validation if not taken into account in the validation. |
|
| Potential source of systematic errors that are correlated in time and space. |
Part III Gap remedies
Gap remedies:
Remedy 1: Instigate a reference quality measurement program for Pandora measurements
Primary gap remedy type:
Research
Secondary gap remedy type:
Technical
Proposed remedy description:
A literature review undertaken in consultation with the Pandora community will provide a better quantification of the measurement uncertainties. This literature review should be supported by findings from the CINDI-2 campaign. Potentially, sensitivity studies to simulate the effects of various uncertainties in the retrieval setup are also needed to fully characterize the uncertainties of the ozone observations. A substantive analysis is required in consultation with experts in metrology to ensure a fully traceable uncertainty can be quantified. This may require modifications to instrument protocols down the line. Key facets of a traceable measurement are: Derivation of measurement equation and traceability diagrams, quantification of effect uncertainties, standardisation of measurement procedures and documentation of the methods deployed.
Within GAIA-CLIM, a detailed traceability chain has already been developed for total column ozone measurements made using UV-visible spectroscopic instruments and for this chain, each of the elements has been described in detail and the corresponding uncertainties have been quantified. Once this traceability chain together with the uncertainty details of the elements have been finalised, this information will be made available publicly and should provide a vital input towards the development of a metrologically rigorous uncertainty quantification for the Pandora instruments. Further work remains to have this processing adopted and the reference quality measurements provided on an operational basis to end-users.
Relevance:
Given that the Pandora instruments will form the backbone of a new measurement network (PANDONIA) run in close collaboration with NDACC, any better understanding of and reduction in the measurement uncertainties will contribute to the homogenisation of the ozone data products available within these networks.
Measurable outcome of success:
The aim is to reduce the total uncertainty of the final ozone data product and to understand the uncertainty budget and to quantify it in a metrological sense.
Expected viability for the outcome of success:
- High
Scale of work:
- Individually
- Single institution
Time bound to remedy:
- Less than 3 years
Indicative cost estimate (investment):
- Low cost (< 1 million)
Indicative cost estimate (exploitation):
- No
Potential actors:
- EU H2020 funding
- Copernicus funding
- National funding agencies
- ESA, EUMETSAT or other space agency
References:
- Herman, J. R., Evans, R. D., Cede, A., Abuhassan, N. K., Petropavlovskikh, I., and McConville, G.: Comparison of Ozone Retrievals from the Pandora Spectrometer System and Dobson Spectrophotometer in Boulder Colorado, Atmos. Meas. Tech., 8, 3407–3418, https://doi.org/10.5194/amt-8-3407-2015, 2015.
- Tzortziou, M., Herman, J. R., Cede, A., and Abuhassan, N.: High precision, absolute total column ozone measurements from the Pandora spectrometer system: Comparisons with data from a Brewer double monochromator and Aura OMI, J. Geophys. Res., 117, D16303, doi:10.1029/2012JD017814, 2012.