This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 640276.
G2.06 Current poor spatial coverage of high-quality multi-wavelength lidar systems capable of characterising aerosols
Submitted by Anna Mikalsen on 9 June, 2017 - 16:09
Gap abstract:
Raman lidars or multi-wavelength Raman lidars are undoubtedly an integral component of an aerosol global measurement infrastructure as they can provide quantitative range-resolved aerosol optical and microphysical properties. It is very important to carefully assess the value of the retrieval of advanced lidar systems and to study if the global coverage of the existing networks is sufficient to carry out adequate satellite-retrieval characterisation. The availability of a larger number of multi-wavelength Raman lidar measurements would strengthen the global observing system for the upcoming research satellite mission Cal/Val (Sentinels 4/5, ADM-Aeolous, Earth-CARE, ACE) and ensure a critical contribution to distinguish natural and anthropogenic aerosols from satellite data. Multi-wavelength Raman lidars could be considered to be the future backbone of a larger network incorporating simpler lidar instruments and/or ceilometers, and so be able to have a denser global spatial coverage.
Part I Gap description
Primary gap type:
- Spatiotemporal coverage
ECVs impacted:
- Aerosols
User category/Application area impacted:
- Operational services and service development (meteorological services, environmental services, Copernicus Climate Change Service (C3S) and Atmospheric Monitoring Service (CAMS), operational data assimilation development, etc.)
- Climate research (research groups working on development, validation and improvement of ECV Climate Data Records)
Non-satellite instrument techniques involved:
- Lidar
Detailed description:
Raman lidars or multi-wavelength Raman lidars are undoubtedly an integral component of an aerosol global measurement infrastructure as they can provide quantitative range-resolved aerosol optical and microphysical properties throughout much of the column. Whereas the detection of aerosol layers and their vertical extent requires only simple single wavelength backscatter lidars, the derivation of extinction coefficient profiles and of a series of derived aerosol properties requires advanced lidar setups and techniques such as high-spectral resolution lidars (HSRL, Shipley et al., 1983) or Raman lidars (Ansmann et al., 1992). The estimation of aerosol microphysical properties and mass concentration requires at minimum a one-wavelength Raman lidar, though the error affecting these estimations can be dramatically reduced if a multi-wavelength Raman lidar system is used. This highlights the relevance of having an enhanced number of multi-wavelength Raman lidars globally if they are to be used to characterise satellite measurements that aim to discern such properties.
Such lidars also have a potential role as anchor reference stations for the study of the impact of aerosols on weather and climate more generally. The availability of multi-wavelength Raman lidar measurements also ensures that ground-based instruments can deliver wavelength conversion information for different aerosol and cloud types to relate the current and future space-borne measurements performed by different satellite missions at different wavelengths (for example, CALIPSO at 532 nm and the future EarthCARE mission at 355 nm). In addition, space-based measurements have the advantage of obtaining global spatial coverage, but long-term ground-based observations can provide a critical contribution to distinguish natural and anthropogenic aerosols from satellite data.
Multi-wavelength Raman lidars could be considered to be the future backbone of a larger network incorporating simpler lidar instruments and/or ceilometers, and so be able to have a denser global spatial coverage. In this process, it is very important to carefully assess the value of the retrieval of advanced lidar systems and to study if the coverage of the existing networks globally is sufficient to carry out a sufficiently accurate aerosol study.
Steps towards automatic or semi-automatic usage of the most advanced lidars are needed to reduce the traditional intensive manpower typically required to operate these systems. In this sense, the effort spent over the last year by the biggest aerosol lidar networks (EARLINET, MPLnet) to develop automatic lidar data processing chain must be acknowledged.
The working groups of lidar network representatives involved in the Aerosol SAG (Scientific Advisory Group) of the WMO-GAW programme has recently started working to address (on voluntarily basis) specific harmonisation issues on the global scale.
Operational space missions or space instruments impacted:
- Copernicus Sentinel 4/5
- Active sensors
Validation aspects addressed:
- Time series and trends
Gap status after GAIA-CLIM:
- After GAIA-CLIM this gap remains unaddressed
Some activities pertinent to this gap have been addressed but the gap could not be solved completely within the timeframe of GAIA-CLIM.
Part II Benefits to resolution and risks to non-resolution
| Identified benefit | User category/Application area benefitted | Probability of benefit being realised | Impacts |
|---|---|---|---|
Improved coverage of aerosol lidar measurements at the global scale |
|
| Increase the accuracy of estimation of aerosol effects on weather and climate; improved monitoring of aerosol related natural hazards e.g. volcanic plumes, dust storms |
Stronger global observing system for the upcoming research satellite Cal/Val (e.g. for missions like ADM-Aeolus, EarthCARE, Sentinels). |
|
| Availability of Fiducial Reference Measurements (FRM) for ensuring the harmonization of satellite data products |
| Identified risk | User category/Application area at risk | Probability of risk being realised | Impacts |
|---|---|---|---|
Lower spatial coverage for satellite validation using Raman lidar measurements |
|
| There is a continuously increasing demand for aerosol products for different applications (climate, weather, satellite, air quality, solar applications, agriculture, health), but quantitative measurements of aerosol microphysical properties in the column can only be provided by Raman lidar systems, the spatial coverage of which is also essential for the calibration of baseline observations (i.e. ceilometers). |
Need for the harmonization of aerosol satellite measurements performed at different wavelengths |
|
| Over coming decades, the number of aerosol satellite missions will increase and this requires the establishment of databases containing the conversion factors to allow a physically consistent use of measurements performed at different wavelengths, as described in Pappalardo et al., 2010 (JGR). The risk is to have non-harmonized CDRs that cannot effectively contribute to the interpretations of global climate change. |
Part III Gap remedies
Gap remedies:
Remedy 1: Improve the coverage, metrological characterisation, and operational capabilities of Raman lidars
Primary gap remedy type:
Deployment
Secondary gap remedy type:
Deployment
Proposed remedy description:
A first step would be to identify existing Raman lidar measuring aerosol properties globally and then subsequently study the representativeness of each station in the characterization of aerosol variability in a range of different vertical atmospheric regions. This would allow the identification of those priority climatic regions where additional multi-wavelength Raman lidars are required and taking advantage of existing lidar station which are not operating a Raman lidar yet.
To make such activities sustainable and operational at the a global scale, many further steps are needed including:
- Establishment of mechanisms for regular communication between networks (under GAW coordination);
- Developing an agreement on a shared/common metadata access portal and automatic product calculation;
- Improving the metrological characterisation of many systems (e.g. existing assessments indicate some potential systematic errors in the aerosol characterisation)
- Developing common harmonised methodologies, data quality objectives, quality assurance/quality control procedures across measurement frameworks to the extent possible;
- Performing frequent intercomparison activities.
Relevance:
A complete remedy for this gap is strongly related to the strategies of the international research institutions which are at present the key players in the deployment and the operation of Raman lidar measurements. A well-defined strategy implementing integration of aerosol measurement capabilities on continental or larger scales will result in clear benefits such as improved data access and availability, improved comparability of data, more uniform data quality standards from different networks, increased synergy of measurements and prevention of unnecessary duplication.
Commercial lidars or ceilometers will benefit of an improved metrological characterization, with a consequent impact of the ingestion of massive higher quality data from low-cost monitoring systems in real-time within weather numerical models.
Measurable outcome of success:
This is obviously related to the establishment of multi-wavelength Raman lidars in those regions where a lack of lidar instruments is identified by a study of representativeness of the existing measurements of aerosol properties. Such study also allows a rationalization of the required investments.
Expected viability for the outcome of success:
- Medium
Scale of work:
- Single institution
- Consortium
Time bound to remedy:
- Less than 5 years
Indicative cost estimate (investment):
- Medium cost (< 5 million)
Indicative cost estimate (exploitation):
- Yes
Potential actors:
- National funding agencies
- ESA, EUMETSAT or other space agency
- Academia, individual research institutes
References:
- Ansmann et al., 1992 Ansmann, Albert & Wandinger, Ulla & Riebesell, Maren & Weitkamp, Claus & Michaelis, Walfried. (1992). Independent measurement of extinction and backscatter profiles in cirrus clouds by using a combined Raman elastic-backscatter lidar. Applied optics. 31. 7113. 10.1364/AO.31.007113.
- HSRL, Shipley et al., 1983
- World Meteorological Organisation, Global Atmosphere Watch, Recommendations for a Composite Surface-Based Aerosol Network. GAW Report No. 207, http://www.wmo-gaw-wcc-aerosol-physics.org/files/gaw-207.pdf.