An overview of volcano infrasound: From hawaiian to plinian, local to global

Volcano infrasound: A review

Climate variability in the high-latitude Southern Hemisphere (SH) is dominated by the SH annular mode, a large-scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex. We present evidence that recent trends in the SH tropospheric circulation can be interpreted as a bias toward the high-index polarity of this pattern, with stronger westerly flow encircling the polar cap. It is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex, which are due largely to photochemical ozone losses. During the summer-fall season, the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the Antarctic Peninsula and Patagonia and to the cooling over eastern Antarctica and the Antarctic plateau.

Interpretation of recent Southern Hemisphere climate change

Rapid mass movements such as avalanches, debris flows, and rock fall are periodic or episodic phenomena that occur in alpine regions. Recent studies have shown that debris flows generate characteristic signals in the low-frequency infrasonic spectrum (4–15 Hz). Infrasound can travel thousands of kilometers and can still be detectable. This characteristic provides a basis for the development of wide area automated monitoring systems that can operate in locations unaffected by the activity of the process. This study focuses on the infrasound vibrations produced by a debris flow at the Lattenbach torrent, Tyrol (Austria), and by two events at the Illgraben torrent, Canton of Valais (Switzerland). The Lattenbach torrent is a very active torrent, which is located in the west of Tyrol in a geologic fault zone between the Silvrettakristallin and the Northern Limestone Alps. It has a large supply of loose sediment. The Illgraben torrent, which is well known for its frequent sediment transport and debris flow activity, has been equipped with instruments for debris flow monitoring since the year 2000. This study shows that debris flow emits low-frequency infrasonic signals that can be monitored and correlated with seismic signals. During the passage of the debris flow, several surges were identified by ultrasonic gauges and detected in the time series and the running spectra of infrasonic data.

Infrasound produced by debris flow: propagation and frequency content evolution

A standardized, self-similar, multiresolution algorithm is developed for scaling infrasonic signal time, frequency, and power within the framework of fractional octave bands. This work extends accepted fractional octave band schemas to 0.001 Hz (1000 s periods) to facilitate the analysis of broadband signals as well as the deep acoustic-gravity and Lamb waves captured by the global infrasound network. The Infrasonic Energy, Nth Octave (INFERNO) multiresolutionEnergy Estimator is applied to computing the total acoustic energy of the Russian meteor signature recorded in the 45mHz-9 Hz frequency band by IMS array 131KZ, Kazakhstan.

/pdf/on-infrasound-standards-part-1-time-frequency-and-energy-4go9vncyrs.pdf

On Infrasound Standards, Part 1 Time, Frequency, and Energy Scaling

The infrasound monitoring is a new technique to study the dynamics of the upper atmosphere. Infrasound waves are reflected by the various atmospheric layers depending on the vertical profile of wind and temperature. The measurement of the characteristics of infrasound signals brings then very useful information on the structure and dynamics of the upper atmosphere. In the IMADYN project proposed to the French Agence National de la Recherche, specialists of atmospheric dynamics and infrasound atmospheric propagation will work together to assess the potential of the IMS network of microbarometers of the Comprehensive Nuclear-Test Ban Treaty-Organisation (CTBT-O), in order to improve our knowledge of the dynamics of the middle and upper atmosphere. The proposal is composed of two parts, the first one based on the exploitation of the existing IMS database in comparison with available meteorological and climatological atmospheric models. The second one is based on the organization of a field campaign at the Haute-Provence Observatory equipped with state of the art lidars and radars systems were microbarometers will be installed for a detailed study of infrasound propagation and atmospheric waves and perturbations.

https://hal.archives-ouvertes.fr/hal-00550905/document

IMADYN : A field campaign to evaluate the potential of infrasound monitoring for atmospheric dynamics studies

Atmospheric gravity waves and turbulence generate small-scale fluctuations of wind, pressure, density, and temperature in the atmosphere. These fluctuations represent a real hazard for commercial aircraft and are known by the generic name of clear-air turbulence (CAT). Numerical weather prediction models do not resolve CAT and therefore provide only a probability of occurrence. A ground-based Rayleigh lidar was designed and implemented to remotely detect and characterize the atmospheric variability induced by turbulence in vertical scales between 40 m and a few hundred meters. Field measurements were performed at Observatoire de Haute-Provence (OHP, France) on 8 December 2008 and 23 June 2009. The estimate of the mean squared amplitude of bidimensional fluctuations of lidar signal showed excess compared to the estimated contribution of the instrumental noise. This excess can be attributed to atmospheric turbulence with a 95% confidence level. During the first night, data from collocated stratosphere-troposphere (ST) radar were available. Altitudes of the turbulent layers detected by the lidar were roughly consistent with those of layers with enhanced radar echo. The derived values of turbulence parameters Cn2 or CT2 were in the range of those published in the literature using ST radar data. However, the detection was at the limit of the instrumental noise and additional measurement campaigns are highly desirable to confirm these initial results. This is to our knowledge the first successful attempt to detect CAT in the free troposphere using an incoherent Rayleigh lidar system. The built lidar device may serve as a test bed for the definition of embarked CAT detection lidar systems aboard airliners.

/pdf/tentative-detection-of-clear-air-turbulence-using-a-ground-naputvlyw2.pdf

Tentative detection of clear-air turbulence using a ground-based Rayleigh lidar.

IMADYN ऀð : ऀð A ऀð field ऀð campaign ऀð to ऀð evaluate ऀð the ऀð potential ऀð of ऀð infrasound ऀð monitoring ऀð for ऀð atmospheric ऀð dynamics ऀð studies

RESUME This paper summarises the status of the GOMOS calibration assessed by the GOMOS CAL/VAL team after nine months of the instrument in-flight life The first GOMOS occultation was successfully measured on March 22, 2002, starting the calibration and verification activity phase Since this date, more than 50000 occultations have been performed until end of 2002 The GOMOS CAL team was in charge of i) the full in-flight calibration and recharacterisation of GOMOS, ii) all the activities required to achieve the complete verification of the level 1b processing models, including: algorithms, auxiliary products, instrument performance, measurements geolocation and validation of the atmosphere related parameters Lastly, the GOMOS CAL team provided the relevant inputs to the GOMOS mission planning monitoring, and to the future routine calibration operations and validation activities The GOMOS instrument in-flight performances are globally very good, in line with expected budget, except for CCD behaviour (hot pixels, RTS) All measured performances are described hereafter, together with assessment methodology and recommendations 1 GOMOS INSTRUMENT PERFORMANCE 11 Brief reminder of the GOMOS instrument measurement concept The GOMOS operating principle relies on the stellar occultation method, which consists to observe a star outside the atmosphere (thus providing a reference stellar spectrum) and track it as it sets through the atmosphere (thus providing spectra with absorption features) When these occulted spectra are divided by the reference spectrum, nearly calibrationfree horizontal transmission spectra are obtained, assuming the instrument response function does not change during one occultation; lasting typically 30 to 40 seconds These transmissions provide the basis for retrieval of atmospheric constituents density profiles, which benefits from the fact that observing the star light confines the measurement to a "thin" well-defined volume 12 Method The verification of the instrument health and performance activities have started on March 22, 2002, just after the SODAP phase which had validated the correct behaviour of the Service Module, Payload Equipment Bay and Payload instruments, checked the GOMOS level 0 products format, and roughly verified that the instrument can be commanded as expected Due to launch and in-orbit environments, several instrument characteristics may have been modified like the instrument response function, thermal distortion and settling of the optical bench,  and this calls for calibration and monitoring of GOMOS parameters behaviour and performance: electronic gain chain, read-out noise and offset, non linearity, dark charge, pixel response non-uniformity, radiometric sensitivity, spectral line spread function, wavelength assignment, vignetting, and straylight All measured performances are described hereafter The method and tools used during the Calibration phase are briefly described Then, the measurement results are analysed and compared to the expectations and the specifications Finally, for each calibration parameter, recommendations are given for the routine mission __________________________________________________________________________________________________________ Proc of Envisat Validation Workshop, Frascati, Italy, 9 – 13 December 2002 (ESA SP-531, August 2003) 13 Acquisition, detection and pointing performance The objective is to verify if the GOMOS instrument is able to acquire and track stars outside and through the atmosphere This task will allow to assess tracking limits (altitude range versus star magnitude) and to verify the dynamic component of the pointing errors that contribute to the dynamic spatial and spectral Line Spread Functions The detection and acquisition performance have been analysed: • during SODAP, for the acquisition and tracking ranges • by analysing the successful acquisition of faint stars The mispointing observed during SODAP is linked with the acquisition cone It has been analysed using the Most Illuminated Pixel position in detection given in the auxiliary data Tracking capability has been analysed using the SATU noise monitoring (auxiliary data) and looking at the altitude corresponding to the tracking loss The tools used for these analyses are mainly the Calibration software CALEX and the GOMOS processing prototype GOPR The acquisition range and tracking Field Of View are consistent with the delivery status Margins have been taken in order to be sure not to hit the limits Table 1: Ranges and duration performance 10 s 2°/s > 2°/s Rallying speed 7°; 5° > 71°; 53° 74°; 65° Tracking FOV -10 – 90° 62 – 68° > -108 – 908° > 62 – 688° -11 – 91° 617 – 69° SFM range spec measured expected Acquisition The duration of rallying and centring phases are also confirmed For the performance in detection, a limited number of stars have been tested and the detection threshold has been kept to a safe value Indeed, a too small value can lead to a class C anomaly which put instrument in Refuse mode Even if there is no danger for the instrument, we decided not to test the limits of detection Indeed, the actual number of tested stars is already much larger than the scientific need (and than the specification) Table 2: Detection probability results 32 > 4 44 Cold star bright limb 16 > 32 22 Hot star bright limb 4 > 45 68 Cold star dark limb 24 > 37 46 Hot star dark limb spec measured expected Detection capability Acquisition mispointing performance is the difference between expected and observed position of the star in the SATU FOV after rallying The expected value is less than 016° The observed value during SODAP is 03° in elevation 'El) and 01° in azimuth (Az) The analysis of the unexpected mispointing in Elevation has shown: • a contribution due to a forgetting of GOMOS optical frame / GOMOS reference cube alignment in the configuration matrix (01° in elevation and 006° in azimuth) • a possible impact of the gravity compensation of the mechanism A shift of a few tens of microns could easily induce a bias of 01° in elevation • a possible contribution due to the calibration curves of SFA angles This difference has been corrected and the stars are now detected at the centre of the SATU No trend has been observed since then (Fig 1) Fig 1: Position of the detection of stars in SATU before and after the correction Tracking noise and robustness: the expected value of the SATU noise equivalent angle in dark limb (at 100 Hz) is 13 μrad (3s) for a specification of 18 μrad The measured value is better than 3 μrad in dark limb (DL) and 10 μrad in bright limb (BL) (35 km altitude) Noise is less than 1 μrad (3σ) for Sirius Fig 2 presents the mispointing error reported by the SATU data Movement in elevation around 100 km is due to the presence of the O2 emission layer The refraction effect can be seen in elevation below 40 km -50 -40 -30 -20 -10 0 10 20 30 40 50 0 20 40 60 80 100 120 140 Elevation Azimuth μrad SATU noise at 100 Hz for Sirius Dark limb km -50 -40 -30 -20 -10 0 10 20 30 40 50 0 20 40 60 80 100 120 140 Elevation Azimuth μrad SATU noise at 100 Hz for ID 154, Bright limb

https://earth.esa.int/pub/ESA_DOC/envisat_val_1202/proceedings/ACV/GOMOS/01_barrot.pdf

GOMOS Calibration on Envisat Status on December 2002

Atmospheric gravity waves and turbulence generate small-scale fluctuations of wind, pressure, density and temperature in the atmosphere. These fluctuations represent a real danger for commercial aircrafts and are known under the generic name of Clear Air Turbulence (CAT). They are not resolved in weather forecast models and are therefore unpredictable. A ground-based Rayleigh lidar was designed and implemented to remotely detect and characterize the atmospheric variability induced by gravity waves and turbulence in vertical scales between 10m and 1000m. Field measurements at Observatoire de Haute-Provence (France) have shown that the built lidar device was actually able to detect episodes of turbulence. This is to our knowledge the first Rayleigh lidar system able to detect clear air turbulence. The built lidar device may serve as a test bed for the definition of embarked CAT detection lidar systems on board airliners.

Charles Cot

Papers

IMADYN : A field campaign to evaluate the potential of infrasound monitoring for atmospheric dynamics studies

Tentative detection of clear-air turbulence using a ground-based Rayleigh lidar.

IMADYN ऀð : ऀð A ऀð field ऀð campaign ऀð to ऀð evaluate ऀð the ऀð potential ऀð of ऀð infrasound ऀð monitoring ऀð for ऀð atmospheric ऀð dynamics ऀð studies

GOMOS Calibration on Envisat Status on December 2002

Set-up of a ground-based Rayleigh lidar to detect clear air turbulence