V043-09
Inversion of acoustic backscatter to estimate hydrothermal diffuse heat
Inversion of acoustic backscatter to estimate hydrothermal diffuse heat
Wednesday, 16 December 2020: 12:02
Virtual
Abstract:
COVIS (Cabled Observatory Vent Imaging Sonar), presently deployed on the OOI Cabled Array at
the ASHES vent eld, has been used to monitor hydrothermal activity, both focused ows (black
smokers) and diffuse ows. The present work examines methods of estimating heat ux density
of diffuse ows by employing ping-to-ping variation of the signals from the COVIS multibeam
sonar. Inversion is accomplished in two stages. In the rst stage empirical acoustic models are
used to estimate the structure function for path-averaged temperature uctuation. In the second
stage parameters characterizing the structure function are used to estimate heat ux density by
means of another empirical model. Adjustable parameters in the structure-function models are
set by comparison with in-situ data obtained using tripod-mounted thermistor arrays deployed
using the ROV JASON. The arrays of primary interest in this application have length 2 m with 10
thermistors having spacing increasing with height. The thermistors have a time constant of 0.1 s,
consistent with the acoustically derived structure function which resolves lags of 0.2 s. The
models for heat ux density have one or more free parameters. Setting these parameters is an
ongoing process relying on heat ux estimates from in-situ measurements as well as values
found in the literature. One question yet to be answered is whether the parameters used in the
two inversion stages apply equally to all the diffuse ows visible to COVIS at ASHES. A longerterm
issue is whether these parameters are applicable more universally to other diffuse-ow
sites.
the ASHES vent eld, has been used to monitor hydrothermal activity, both focused ows (black
smokers) and diffuse ows. The present work examines methods of estimating heat ux density
of diffuse ows by employing ping-to-ping variation of the signals from the COVIS multibeam
sonar. Inversion is accomplished in two stages. In the rst stage empirical acoustic models are
used to estimate the structure function for path-averaged temperature uctuation. In the second
stage parameters characterizing the structure function are used to estimate heat ux density by
means of another empirical model. Adjustable parameters in the structure-function models are
set by comparison with in-situ data obtained using tripod-mounted thermistor arrays deployed
using the ROV JASON. The arrays of primary interest in this application have length 2 m with 10
thermistors having spacing increasing with height. The thermistors have a time constant of 0.1 s,
consistent with the acoustically derived structure function which resolves lags of 0.2 s. The
models for heat ux density have one or more free parameters. Setting these parameters is an
ongoing process relying on heat ux estimates from in-situ measurements as well as values
found in the literature. One question yet to be answered is whether the parameters used in the
two inversion stages apply equally to all the diffuse ows visible to COVIS at ASHES. A longerterm
issue is whether these parameters are applicable more universally to other diffuse-ow
sites.