1. ACCENT Symposium Sept. 17-20,Urbino (Italy) CEILOMETER FOR THE AEROSOL PROFILING: OPPORTUNITIES AND LIMITS Fabio Madonna, Ioannis Binietoglou, D’Amico Giuseppe, Gelsomina Pappalardo Consiglio Nazionale delle Ricerche, Istituto di Metodologie per l’Analisi Ambientale (CNR-IMAA) fabio.madonna@imaa.cnr.it

2. ACCENT Symposium Sept. 17-20,Urbino (Italy) Lidar Techniques Raman and HSRL: α+β with no assumption on the lidar ratio S (only angstrom coefficient assumed with very low errors) Advanced lidar technique (multi-wavelength) Elastic: β using Klett or Fernald methods, assumption of S, constant throughout the profile. Basic lidar technique: backscatter lidars and ceilometers (using ancillary measurements)

3. Advanced lidars ACCENT Symposium Sept. 17-20,Urbino (Italy) From multi-wavelenght Raman lidars it is possible to calculate secondary optical data: Color ratios β(1064 nm)/β(532 nm) β(532 nm)/β(355 nm) α(532 nm)/α(355 nm) Lidar ratios (355, 532 nm) Ångström exponents α-related Β-related Chacterization of whole uncertainty budget.

4. ACCENT Symposium Sept. 17-20,Urbino (Italy) Moreover we can: ► Check whether these data make sense in the present scenario. ► Re-evaluate your data, if you find “strange“ results!!! ► In one word, “quality assurance”. From multi-wavelenght Raman lidars it is possible to calculate secondary optical data: Color ratios β(1064 nm)/β(532 nm) β(532 nm)/β(355 nm) α(532 nm)/α(355 nm) Lidar ratios (355, 532 nm) Ångström exponents α-related Β-related Chacterization of whole uncertainty budget. Advanced lidars

5. Werner Ceilometers for aerosol profiling: potential world ceilometer network ACCENT Symposium Sept. 17-20,Urbino (Italy) Courtesy of W. Thomas

6. ACCENT Symposium Sept. 17-20,Urbino (Italy) Ceilometers for aerosol profiling: potential world ceilometer network

7. Werner ACCENT Symposium Sept. 17-20,Urbino (Italy) … focus on Europe

8.   From two independent measurements ¥ ¥ Identification of scattering type (aerosol particles, cloud droplets, ice crystals, some aerosol type information) ‡ ‡ A ceilometer is a single- wavelength, low-power lidar, with lower S/N ratio § § if calibrated [1] [1] Estimate only # # m > 2 [2] [2] Most Raman lidar systems operate during night-time. 24h Raman lidar systems exist and their operability has been proved, however few systems nowadays operate Raman channels also during daytime; HSRL is independent of daytime. d= only daytime, n= only night time Official Request for Provision of a Table of Capabilities and Accuracies of Detection Methods based on ICAO- IVATF/2 WP05 Ground- based Lidar techniques Geo. propert ies aa aa SS AODåå åå type ¥ ¥ Microphys. prop. ceilometer ‡ ‡ §§ Ceilo+sun photo.   (d) Ceilo+sun photo.+ depol   (d) 1  (d)  (limited) Backscatter lidar 1-λ  Backscatter lidar 1-λ + sun photo.   (d) 1  (d) Backscatter lidar 1-λ + sun photo.+ depol   (d) 1  (d)  (d) (limited) Backscatter lidar m-λ ♯ ♯  Backscatter lidar m-λ ♯ + sun photo.   (d) 1  (d)  (d) 1  Backscatter lidar m-λ ♯ + sun photo.+ depol   (d) 1  (d)  (d) 1  Ceilometer profiling … which products can be retrieved using a ceilometer… ACCENT Symposium Sept. 17-20,Urbino (Italy)

9. Aerosol detection ACCENT Symposium Sept. 17-20,Urbino (Italy) Comparison of the arrival time of the first ash cloud over Europe on 16 and 17 April 2010 from ceilometer observations from the DWD ceilonet (circles) and from MCCM simulation (shading). The arrival times refer to 3 km height. The colours indicate the arrival times (6 h intervals, scale to the right). Black circles indicate sites without measurements, white circles that no ash cloud could be detected at this site. Emeis et al.: The 16/17 April 2010 Eyjafjallajökull volcanic ash layer dispersion

10. Backscattering coefficient This is the only product that can be inferred from ceilometer data. Several algorithms have been proposed and classified as: → FORWARD approaches: use a backscattering reference to calculate the calibration constant PROS: ancillary co-located Raman lidar measurements only for short periods CONS: only cloud free, periodic re-calibration, long time a veraging (~ 2 h) → BACKWARD approaches: use ancillary estimation of lidar ratio or aerosol optical thickness (AOD) PROS: use of ancillary measurements from sun photometer nephelometer (automatic and low-cost devices) CONS: need for ancillary measurements of AOD (daytime), mainly in clear skies, long time averaging (> 2-3 h) ACCENT Symposium Sept. 17-20,Urbino (Italy)

11. … potential discrepancies on various products not “easy” to be retrieved using a ceilometer though using several assumptions… Backscattering: > 10 - 20 % (Wiegner et al., 2012), but need to checked over large datasets (calibration error highly relevant!) Extinction: > Backscattering discrepancy + lidar ratio assumption (even larger than 50 %) Effective radius: < 50 % using 4 backscattering profiles with σ β <10% (Veselovsky et al., 2008) Mass concentration: > Extinction discrepancy ACCENT Symposium Sept. 17-20,Urbino (Italy)

12. Aerosol layering PEARL 1064 nm ramge corrected signal CHM15k 1064 nm ramge corrected signal Height (m a.g.l.) 7.5 6.0 4.5 3.0 1.5 0.0 u.a. AOD 532nm = 0.12 20 21 22UTC

13. CT25k not sensitive to aerosol layers in the FT ACCENT Symposium Sept. 17-20,Urbino (Italy) Sensitivity: layer detection

14. % of layers observed by MUSA lidar in 2010 at CIAO Observatory (Potenza) but also detected by the ceilometer - Above 5 km no sensitivity - Nighttime < 5km, Day < 3km ACCENT Symposium Sept. 17-20,Urbino (Italy)

15. Attenuated backscattering ACCENT Symposium Sept. 17-20,Urbino (Italy) Frequency of occurrence of attenuated backscattering values for simultaneous observations performed by MUSA lidar and CHM15k ceilometer in 2010 at CIAO Observatory (Potenza) ► Only night time only observations. ► Same vertical and time resolutions. ► Differences below 2.0 km due to overlap and detection issues ► Better agreement above 2.0 km

16. Beta vs Alfa vs Height ACCENT Symposium Sept. 17-20,Urbino (Italy) MUSA lidar observation, 2010, CIAO 355 nm extinction coefficient from MUSA

17. ACCENT Symposium Sept. 17-20,Urbino (Italy) Beta vs Alfa vs Height CHM15k ceilometer observation, 2010, CIAO 355 nm extinction coefficient from MUSA

18. ACCENT Symposium Sept. 17-20,Urbino (Italy) Beta vs Alfa vs Height CHM15k ceilometer observation, 2010, CIAO Lower values with increasing height and extinction (low SNR) 355 nm extinction coefficient from MUSA

19. ACCENT Symposium Sept. 17-20,Urbino (Italy) Summary Ceilometers show a good potential for aerosol profiling but they are limited: Aerosol detection: ► promising in synergy with lidars and/or transport/chemical models. Aerosol optical and microphysical properties: ► backscattering coefficient only Aerosol layering in the lower tropopshere: ► feasible but sensitivity limited in the free troposphere Ceilometers as an aerosol observation technology ► improvements are needed for both the receiver and detection parts

20. Ceilometers in network around an anchor station ACCENT Symposium Sept. 17-20,Urbino (Italy)

21. Thanks Acknowledgements The financial support of European Commission grants RICA-025991 EARLINET- ASOS and 262254 ACTRIS, and the financial support of the national project “Programma Operativo Nazionale (PON) – Regione Basilicata 2000/2006” are gratefully acknowledged. This work has been also partially supported by the EU FP7 project WEZARD (Weather hazards for aeronautics) grant agreement no. 285050.