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

Abstract

Abstract. 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 measurements 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.

A Multi-Sensor Approach for Volcanic Ash Cloud Retrieval and Eruption Characterization: The 23 November 2013 Etna Lava Fountain

“…R HV (unitless) is the modulus of the correlation coefficient between horizontal-polarized (H) and vertical-polarized (V) signals, and it describes the target heterogeneity within the radar resolution cells, while W (m 2 /s 2 ) is an indication of the diversity of the particle radial velocities. For a robust theoretical background in the meaning of radar variables, see Bringi et al [26], and for exploitation of radar polarimetry in relation to ash clouds, see Vulpiani et al [27], Montopoli et al [28] and Crouch et al [29].…”

“…The former include C a , M a and R e , while the latter include h ct and ∆h ct . The volcanic ash radar retrieval (VARR) procedure, developed in Marzano et al, 2006 [30], and subsequently applied to polarimetric data by Vulpiani et al [27] and Montopoli et al [28], is used to define the microphysical characteristics of an ash cloud from radar data. The VARR is based on forward electromagnetic simulations of ash particles in the microwave region assuming a Gamma size distribution model of oblate particles with the random orientation, axis ratio, permittivity and canting angle as specified in [31,32].…”

Velocity profiles inside volcanic clouds from three‐dimensional scanning microwave dual‐polarization Doppler radars

“…The rigorous theoretical background regarding the origin of these variables can be found in Bringi and Chandrasekar [2001], while their interpretation with respect to the tephra clouds has been investigated in Vulpiani et al [2011], Montopoli et al [2014a], and Crouch et al [2014]] and will be discussed here in relation to the Etna case study in the following section. The Appendix A in this work summarizes the mathematical definitions of the radar variables used.…”

Overview: Tropospheric profiling: state of the art and future challenges – introduction to the AMT special issue

“…Lolli et al (2013) suggested the validation approach for the planned ESA Aeolus mission. Several authors (Burton et al, 2013;Bayat et al, 2013;Nemuc et al, 2013;Montopoli et al, 2014) pointed out that the information brought by multi-wavelength, dualpolarization observations should be further investigated by both experimental data and modeling. In order to consolidate demonstrative results, statistically significant data sets from long time periods (Pichelli et al, 2014) or from dedicated field experiments (Chen et al, 2013) deploying remote sensing observations should be considered.…”

“…A simple relationship between the reflectivity factor and kinetic energy fluxes is found for each case study. Montopoli et al (2014) discuss the potentiality and drawbacks of X-band dual-polarization (DPX) radar measurements to estimate near-source volcanic ash cloud parameters. They present data acquired during the Grímsvötn (Iceland) volcanic eruptions in May 2011.…”