Monitoring and scientific analysis of aerosol column integrated properties in the Indian Ocean.

Marion Dufresne Atmospheric Program Indian Ocean 
MAP-IO
 

A ship-borne sun/sky/lunar-photometer of Cimel CE318T type was set up permanently, in the frame of the French MAP-IO research program, early January 2021, onboard the French research vessel Marion Dufresne (Fig. 1). It will be operated mainly in the Southern Hemisphere / Indian Ocean. Since the first preparatory campaigns (i) AQABA (2017), in the Mediterranean and Arabian basins (Unga et al., 2019), (ii) OCEANET (2018, 2019) with trans-Atlantic cruises aboard the German vessel Polarstern, (Yin et al., 2019), (iii) SEA2CLOUD in the Indian ocean (2020), the system has been tested, improved and validated to measure aerosol optical depth (AOD) and column-mean Ångström coefficient  (Yin et al., 2019; Popovici et al., 2019). 

Short technical Description

The ship-borne CE318-T shown in Fig. 1 was developed to enable AOD measurements on mobile platforms and to expand and automatize the AERONET coverage to the vast ocean area (Goloub et al., 2017), currently manually operated within the MAN branch of AERONET (Smirnov et al., 2009). The system is composed of the optical head, rotational base, control unit, air-pumping component, weather stop component, GPS-based compass and positioning system modules (date, time, geo-location, heading, pitch and roll). The optical head is the standard CE318-T with version 1 of the ship-borne software. The GPS receivers were fixed on the platform together with the photometer robot to assure the same motions. 

In order to track the sun continuously, the system first targets the sun with the last received time, geo-location, heading, pitch and roll information. When the sun enters in the tracking system field-of-view, the photometer switches into tracking mode like a regular photometer, however the tracking feedback loop has been accelerated. The same procedure is applied for the moon triplet as well. The air-pumping module generates compressed dry-cleaned air to the collimator to prohibit the contamination of the optical window by ambient sea spray. Sky radiances in the almucantar geometry are also measured. Time, heading, pitch and roll are measured for each angle to have accurate and precise knowledge of the observation geometry required for further processing. 

Preliminary results from MAP-IO

Data are transmitted via satellite to LOA/CNRS server at Day+1, sent to AERONET. Data are currently processed by LOA to produce spectral AOD, water vapor content, Angström exponent and sky radiance. First level 1.5 AOD are presented in Fig. 2. 

Next Steps and perspectives

• The system will again be improved during the MAP-IO operation (comparison/integration of ancillary data from other onboard instruments (pressure, other navigation system), in the frame of AGORA-Lab, a joint partnership program between CNRS-LOA and CIMEL SME.  
• Analysis of sky radiance to further jointly invert spectral AOD and sky radiances, started during the ESA/IDEAS program, is under progress in the frame of several national and European programs such as ESA/QA4EO, AERONET, ACTRIS, Labex CaPPA.  
• Dedicated processing chain is under-development and could be later implemented into the ACTRIS Data Center for future mobile platforms.
• This automatic ship-borne CE318T photometer will be a good candidate to contribute to satellite Cal/Val activity of current and coming earth observation missions. It is now foreseen that several research or commercial vessels could be equipped with this system and continuously measuring and monitoring aerosol properties over the Oceans.  
• Knowing that this AERONET compatible ship-borne CE318T is performing radiance measurement, one can imagine that future version could target the ocean surface as well, possibly measuring water-leaving radiance. 
• Integration of an automatic lidar system, ideal companion of photometer and in situ aerosol measurements.

Contacts

Philippe Goloub (Science, Philippe.Goloub@univ-lille.fr)

Luc Blarel (Techn., Luc.Blarel@univ-lille.fr)

Reference

1. Goloub, P., Blarel, L., Dubois, G., Popovici, I., Podvin, T., Torres, B., Victori, S., Maupin, F., and Pikridas, M.: Current results on mobile system prototype development for Aerosol Cal/Val activities, ESA/IDEAS Project WP 3440-1/3/5, 12 December 2017. 
2. Yin, Z., Ansmann, A., Baars, H., Seifert, P., Engelmann, R., Radenz, M., Jimenez, C., Herzog, A., Ohneiser, K., Hanbuch, K., Blarel, L., Goloub, P., Dubois, G., Victori, S., and Maupin, F.: Aerosol measurements with a shipborne Sun–sky–lunar photometer and collocated multiwavelength Raman polarization lidar over the Atlantic Ocean, Atmos. Meas. Tech., 12, 5685–5698, https://doi.org/10.5194/amt-12-5685-2019, 2019
3. Unga F., Popovici, I-E, Dubois, G., Blarel L., Pikridas M., Vouterakos P., Sciare J., Goloub P., Torres B., Victori S., Maupin F, Canini M., Mortier A., Lelieveld J., Mobile ship-borne sun/sky/lunar photometer and ceilometer observations during the AQABA campaign, Geophysical Research Abstracts, 2019, Vol. 21.
4. Smirnov, A., B. N. Holben, I. Slutsker, D. M. Giles, C. R. McClain, T. F. Eck, S. M. Sakerin, A. Macke, P. Croot, G. Zibordi, P. K. Quinn, J. Sciare, S. Kinne, M. Harvey, T. J. Smyth, S. Piketh, T. Zielinski, A. Proshutinsky, J. I. Goes, N. B. Nelson, P. Larouche, V. F. Radionov, P. Goloub, K. Krishna Moorthy, R. Matarrese, E. J. Robertson, and F. Jourdin (2009), Maritime Aerosol Network as a component of Aerosol Robotic Network, J. Geophys. Res., 114, D06204, doi:10.1029/2008JD011257
5. Tulet P. et al., Marion Dufresne Atmospheric Program, Indian Ocean (MAP-IO), Surveillance, bancarisation et exploitation scientifique des données atmosphériques sur l’océan Indien dans un contexte changement climatique, LACY, Université de la Réunion, 2019 (https://lacy.univ-reunion.fr/map-io).
6. Popovici, I., Goloub, P., Blarel, L., Podvin, T., Dubois, G., Torres, B., Victori, S., Maupin, S., Ducos, F., Loisil, R., Delegove, R., Unga, F., Pikridas, M., Sciare, J., Yin, Z., Baars, H. Mobile systems for aerosol remote sensing: Development, Evaluation and Data Processing by LOA using ACTRIS/non ACTRIS data, ACTRIS-2 workshop, Darmstadt/EUMETSAT, 2019.