Interpretation of observed microwave signatures from ground dual polarization radar and space multi frequency radiometer for the 2011 Grímsvötn volcanic eruption

M. Montopoli, G. Vulpiani, D. Cimini, E. Picciotti, F. S. Marzano
2013 Atmospheric Measurement Techniques Discussions  
The important role played by ground-based microwave weather radars for the monitoring of volcanic ash clouds has been recently demonstrated. The potential of microwaves from satellite passive and ground-based active sensors to estimate near-source volcanic ash cloud parameters has been also proposed, though with little investigation of their synergy and the role of the radar polarimetry. The goal of this work is to show the potentiality and drawbacks of the X-band dual polarization (DPX) radar
more » ... easurements through the data acquired during the latest Grímsvötn volcanic eruptions that took place in May 2011 in Iceland. The analysis is enriched by the comparison between DPX data and the observations from the satellite Special Sensor Microwave Imager/Sounder (SSMIS) and a C-band single polarization (SPC) radar. SPC, DPX, and SSMIS instruments cover a large range of the microwave spectrum, operating respectively at 5.4, 3.2, and 0.16-1.6 cm wavelengths. The multi-source comparison is made in terms of total columnar concentration (TCC). The latter is estimated from radar observables using the "volcanic ash radar retrieval" algorithm for dual-polarization X-band and single polarization C-band systems (VARR-PX and VARR-SC, respectively) and from SSMIS brightness temperature (BT) using a linear BT-TCC relationship. The BT-TCC relationship has been compared with the analogous relation derived from SSMIS and SPC radar data for the same case study. Differences between these two linear regression curves are mainly attributed to an incomplete observation of the vertical extension of the ash cloud, a coarser spatial resolution and a more pronounced non-uniform beam-filling effect of SPC measurements (260 km away from the volcanic vent) with respect to the DPX (70 km from the volcanic vent). Results show that high-spatial-resolution DPX radar data identify an evident volcanic plume signature, even though the interpretation of the polarimetric variables and the related retrievals is not always straightforward, likely due to the possible formation of ash and ice particle aggregates and the radar signal impairments like depolarization or non-uniform beam filling that might be caused by turbulence effects. The correlation of the estimated TCCs derived from DPX or SPC and SSMIS BTs reaches approximately −0.7.
doi:10.5194/amtd-6-6215-2013 fatcat:ojmzccl7lvcjxkr4m5onyujdze