An evaluation of volcanic cloud detection techniques during recent significant eruptions in the western ‘Ring of Fire’

We examined recent volcanic cloud events in the Western Pacific and Indonesian area, to validate the performance of remote sensing techniques used to support the International Airways Volcano Watch (IAVW). Five events were considered, during which eruptions from eight volcanoes injected ash into the upper troposphere or lower stratosphere. For one of the eruptions, at Miyakejima, Japan, at least five aircraft encountered volcanic ash clouds, and the cost to three operators alone exceeded US $12,000,000 in aircraft repairs, diversions, and lost operating time. We performed ‘reverse’ absorption and ‘pattern analysis’ using GMS-5/VISSR, MODIS and AVHRR data, and we examined TOMS SO₂ and Aerosol Index data, surface-based observations, pilot reports, and dispersion model output. Our results verify that the introduction of ‘reverse’ absorption using the geostationary GMS-5 platform significantly enhanced our capacity to monitor volcanic ash clouds in the region. In one case, we tracked an eruption cloud for approximately 80 h. The primary impediment to remote monitoring is the presence of overlying cloud, or substantial amounts of ice within the volcanic clouds. TOMS data showed success in identifying volcanic clouds during these conditions, but was limited by the infrequency of observations. More effective future operation of the IAVW relies on developing complementary methods of volcanic cloud remote sensing, and greatly increasing the amount and quality of available surface and air observations, including observations of precursor activity. An understanding of the likely future limitations of remote sensing techniques will aid in the refining of IAVW procedures.     

Observations of volcanic ash clouds in the 10-12 μm window using AVHRR/2 data

Abstract

Volcanic aerosols are always present in the atmosphere, but because of the nature of volcanic activity their abundance varies greatly with time. The problem of detecting and monitoring volcanic ash clouds using radiance measurements from the AVHRR/2 (Advanced Very High Resolution Radiometer) instrument is discussed and some results are presented for the Galunggung eruptions of July 1982. It is shown that during the first few hours of an explosive eruption AVHRR/2 thermal channel measurements can be used to detect and discriminate volcanic clouds. Once the eruption cloud has spread and thinned out however, the problem of detection is difficult because of the similarity between dispersed volcanic cloud and semi-transparent cirrus. In these cases, if the volcanic cloud consists of liquid H₂SO₄ droplets, then it is possible to discriminate them from water/ice clouds because of the reverse absorption effect in channel-4 and channel-5. Some evidence is presented showing this effect. It is proposed that the temperature difference image be used operationally to warn of the presence of volcanic clouds.     

A near real-time dual-band-spatial approach to determine the source of increased radiance from closely spaced active volcanoes in coarse resolution satellite data

Bezymianny and Kliuchevskoi volcanoes (Kamchatka) present a danger as both inject ash into North Pacific air routes. Current automated monitoring algorithms do not distinguish them in real time due to their mutual proximity (10 km) and poor geolocation accuracy of Advanced Very High Resolution Radiometer (AVHRR) data. Contrasting mid- and thermal infrared volcanic radiances are influenced by (1) differences in temperature and eruptive style of Bezymianny's andesite and Kliuchevskoi's basalt and (2) different temperatures of the non-volcanic portion of pixels located over their summits, due to different elevations. Data from 571 AVHRR images show the latter is more significant. Discriminant function analysis using summit and regional band 4 pixel-integrated radiant temperatures (pirT) correctly identifies the source volcano of a thermal anomaly in 89% of cases. Weather permitting, a spatial component can be added, leading to improved accuracy. The approach used here can also be applied at other closely spaced volcanoes with substantially different summit elevations.     

An advanced video-based system for monitoring active volcanoes

Video surveillance systems are consolidated techniques for monitoring eruptive phenomena in volcanic areas. Along with these systems, which use standard video cameras, people working in this field sometimes make use of infrared cameras providing useful information about the thermal evolution of eruptions. Real-time analysis of the acquired frames is required, along with image storing, to analyze and classify the activity of volcanoes. Human effort and large storing capabilities are hence required to perform monitoring tasks.In this paper we present a new strategy aimed at improving the performance of video surveillance systems in terms of human-independent image processing and storing optimization. The proposed methodology is based on real-time thermo-graphic analysis of the area considered. The analysis is performed by processing images acquired with an IR camera and extracting information about meaningful volcanic events.Two software tools were developed. The first provides information about the activity being monitored and automatically adapts the image storing rate. The second tool automatically produces useful information about the eruptive activity encompassed by a selected frame sequence.The software developed includes a suitable user interface allowing for convenient management of the acquired images and easy access to information about the volcanic activity monitored.     

Thermal imaging of Nisyros volcano (Aegean Sea) using ASTER data: estimation of radiative heat flux

A time series of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images (AST08) have been processed to allow radiative heat flux estimations of the Nisyros volcano. ASTER night-time images were acquired on four different dates: 7 April 2001, 13 June 2002, 26 October 2002 and 23 July 2005. The results show a steady state energy release with heat fluxes ranging from 15 to 30 W m^?2 over the craters of Kaminakia, Polyvotis and Stefanos, respectively. It is suggested that this range of values indicates a background heat flux of this volcano following the unrest of 1995–1997, and that the volcano has entered again into the quiet phase. Also, on the basis of the average spatial extent of the thermal anomaly a total radiative heat flux of 36 MW was estimated at the moment of ASTER overpass. Heat flux values for Nisyros are in good agreement with other published estimates derived from low-temperature fumarolic volcanoes (Stromboli and Vulcano, Italy) using Landsat TM data. It is also evidenced that the ASTER radiometer can be used as an important imaging tool for the monitoring of geophysical properties associated to volcanic activity, as is the volcanic heat flux.     

ASTER and field observations of the 24 December 2006 eruption of Bezymianny Volcano, Russia

An explosive eruption occurred at Bezymianny Volcano (Kamchatka Peninsula, Russia) on 24 December 2006 at 09:17 (UTC). Seismicity increased three weeks prior to the large eruption, which produced a 12–15 km above sea level (ASL) ash column. We present field observations from 27 December 2006 and 2 March 2007, combined with satellite data collected from 8 October 2006 to 11 April 2007 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), as part of the instrument's rapid-response program to volcanic eruptions. Pixel-integrated brightness temperatures were calculated from both ASTER 90 m/pixel thermal infrared (TIR) data as well as 30 m/pixel short-wave infrared (SWIR) data. Four days prior to the eruption, the maximum TIR temperature was 45 °C above the average background temperature (− 33 °C) at the dome, which we interpret was a precursory signal, and had dropped to 8 °C above background by 18 March 2007. On 20 December 2006, there was also a clear thermal signal in the SWIR data of 128 °C using ASTER Band 7 (2.26 μm). The maximum SWIR temperature was 181 °C on the lava dome on 4 January 2007, decreasing below the detection limit of the SWIR data by 11 April 2007. On 4 January 2007 a hot linear feature was observed at the dome in the SWIR data, which produced a maximum temperature of 700 °C for the hot fraction of the pixel using the dual band technique. This suggests that magmatic temperatures were present at the dome at this time, consistent with the emplacement of a new lava lobe following the eruption. The eruption also produced a large, 6.5 km long by up to 425 m wide pyroclastic flow (PF) deposit that was channelled into a valley to the south–southeast. The PF deposit cooled over the following three months but remained elevated above the average background temperature. A second field investigation in March 2007 revealed a still-warm PF deposit that contained fumaroles. It was also observed that the upper dome morphology had changed in the past year, with a new lava lobe having in-filled the crater that formed following the 9 May 2006 eruption. These data provide further information on effusive and explosive activity at Bezymianny using quantitative remote sensing data and reinforced by field observations to assist in pre-eruption detection as well as post-eruption monitoring.     

ASTER- and field-based observations at Bezymianny Volcano: Focus on the 11 May 2007 pyroclastic flow deposit

Bezymianny (Kamchatka Peninsula, Russia) is an active stratovolcano, characterized by a summit lava dome and overlapping pyroclastic flow (PF) deposits to the southeast. Three explosive eruptions (24 December 2006, 11 May 2007, and 14 October 2007) generated PFs that were dominated by juvenile material and were emplaced primarily due to column collapse. Following this, a gravitational lava flow front collapse event generated block and ash flow on 5 November 2007. Moderate spatial resolution data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument were collected between October 2006 and December 2007 to assist in post-eruption monitoring and interpretation of the volcanological processes that produced the PF deposits. Using multitemporal ASTER thermal infrared (TIR) data, three periods of increased activity were observed that coincided with each eruption and subsequent activity. During a field campaign in August 2007, the May 2007 PF deposit was investigated in detail. Eight ASTER TIR pixels (90 m spatial resolution) were selected from the 30 June 2007 ASTER TIR image, seven of which were accessible in the field. Forward-Looking Infrared (FLIR) image and thermocouple data over these areas were collected to observe thermal heterogeneities with distance along the PF deposit. Although synchronous ASTER data were not possible at the time of fieldwork due to cloud cover, a field survey of blocks versus ash in each pixel was carried out to investigate thermal and textural variation with distance from the vent and to provide preliminary field results. Based on the field-derived temperature data and surface block percentages, the May 2007 PF deposit was more block-rich in the medial portion of the flow surface, but more ash-dominated at the PF terminus region, which promoted more rapid cooling. We present multitemporal ASTER data spanning a 14 month period and highlight ground-based observations acquired within the same period of eruptive and dome-growth activity. These data collectively provide thermal radiative and emissivity information on an actively changing explosive volcanic system and specifically documents changes over recently-emplaced and cooling PF deposits.     

Studying the thermal anomaly before the Zhangbei earthquake with MTSAT and meteorological data

The occurrence of a thermal anomaly before an earthquake has been widely reported in the last 20 years. In these reports, Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS) night-time data are the most widely used data, and the distance between the thermal anomaly and the epicentre is about 100–1000 km. Here we use Multi-functional Transport Satellite (MTSAT) -1R geostationary data, with high temporal resolution and surface air temperature data, to study the thermal anomaly before the Zhangbei earthquakes in China. The combination of these two datasets showed some advantages over AVHRR and MODIS data – they are less affected by clouds, while the surface air temperature difference showed a good relation between the epicentre and thermal anomaly. Their distance is less than 100 km. This provides a possible way to estimate future epicentres within reasonable errors.     

Technical note: Lineament detection on Mount Cameroon during the 1999 volcanic eruptions using Landsat ETM

A study of the active Mount Cameroon volcano, located south west along the Cameroon Volcanic Line, was carried out during the 1999 volcanic eruption, using Landsat Enhanced Thematic Mapper (ETM) imagery. It investigated geologic deformations expressed as faults, cracks and lineaments resulting from the eruption. Various image processing techniques were tested and compared in order to detect the most effective output. Principal Component Analysis was found to be useful to determine the extent of deformations caused during the 1999 volcanic eruptions. Landsat ETM revealed the formation of faults and lineaments with proximity to eruption vents. The interpretation obtained from satellite imagery was cross checked with field and ground truthing data. This paper identifies the dimensions and orientations of the newly formed geologic features.     

Thermal IR satellite sensor data application for earthquake research in China

NOAA/AVHRR thermal images indicated the presence of positive thermal anomalies that are associated with the large linear structures and fault systems of the Earth's crust. The relation between thermal anomalies and seismic activity was established for Middle Asia on the basis of a 7-year series of thermal images. Thermal anomaly has been located near Beijing, on the border between the mountains and plain. The size of this anomaly is about 700 km long and 50 km wide. The anomaly appeared about 6-24 days before and continued about a week after an earthquake. The anomaly was sensitive to crust earthquakes with a magnitude more than 4.7 and for a distance of up to 500 km. The amplitude of this anomaly was about 3 C.     

Automated volcanic hot-spot detection based on FY-4A/AGRI infrared data

ABSTRACT

A new algorithm (FYVOLC) for the automated detection of volcanic hot spots using data obtained from China’s new-generation satellite FY-4A is developed and tested. FYVOLC improves the detection ability of the Volcanic Anomaly SofTware (VAST) algorithm by incorporating a Normalized Brightness Temperature Difference Index (NBTDI) to reduce the influence of ‘cold’ cloud. In addition, FYVOLC introduces a mid-infrared brightness temperature criterion to identify volcanic hot spots by making calculations based on the image itself without artificially determining any parameters. To test the volcanic hot-spot detection performance of FYVOLC, FY-4A Advanced Geostationary Radiation Imager data were used for eruptions from four volcanoes: Mayon Volcano in the Philippines (25–26 January 2018), and Bromo (1–2 September 2018), Lawu (3–4 September 2018), and Soputan volcanoes (3–4 October 2018) in Indonesia. A total of 147 images of the above four volcanoes were used, and the results obtained using the FYVOLC algorithm were compared with those from three existing volcanic hot-spot detection algorithms: the simplified contextual, VAST, and HOTSAT algorithms. It is shown that the simplified contextual and VAST algorithms are prone to generating false alerts (with a maximum false alert rate of up to 41% and 48%, respectively), whereas the simplified contextual and HOTSAT algorithms are prone to missing hot-spot pixels (with a maximum miss rate of up to 71% and 54%, respectively). The FYVOLC algorithm has the best detection accuracy owing to the adopted NBTDI and image-based mid-infrared brightness temperature criterion. The maximum false alert rate of FYVOLC is 12%, and the maximum miss rate is 11%. By analysing the thermal anomaly time-series of the 147 images, it was found that the detection results of FYVOLC are basically consistent with the actual hot spots, except for some images that were strongly affected by cloud cover. This study is the first to realize the automated detection of volcanic hot spots and monitor temporally dynamic thermal phenomena based on FY-4A satellite data. The results have significance for the continuing development of global volcanic early-warning systems and for the dynamic monitoring of volcanoes after eruptions.     

The long-term monitoring of vegetation cover in the Amazonian region of northern Brazil using NOAA-AVHRR data

We have analysed monthly composites of normalized difference vegetation index (NDVI) calculated from NOAA's Advanced Very High Resolution Radiometer (AVHRR) for the Amazonian region of northern Brazil across a decade (August 1981 to June 1991) to ascertain if the dominant vegetation types could be differentiated,and to seek inter-annual climatic variation due to changing environmental conditions. The vegetation types observed included dense forest ( submontana and terras baixas ), open forest ( submontana and terras baixas ), transitional forest, seasonal forest ( caatinga ), and two types of savanna ( cerrado ). We found that monthly NDVI composites revealed seasonality in cerrado and especially in caatinga cover types, which can be used in their identification, whilst the phenology of other forest cover types varies little throughout the year. Additionally, yearly composite NDVI values showed a clear and significant reduction ( p 0.95) in dry years, such as those with El Nino Southern Oscillation events. These results indicate the potential use of multi-temporal NDVI data for the environmental characterization and identification of forest ecosystems. Our research found NDVI images from NOAA AVHRR offer a long-term data set that is unequalled for monitoring terrestrial land cover. However, these data have to be used with a degree of caution, especially in regards to atmospheric interference, such as cloud contamination and volcanic eruptions, and post-launch changes in calibration.     

Remote monitoring of Indonesian volcanoes using satellite data from the Internet

The Internet now harbours vast amounts of cheap and potentially useful remote sensing data. Advanced Very High Resolution Radiometer (AVHRR) data are being increasingly used for volcano surveillance, and the provision of AVHRR Global Area Coverage (GAC) imagery at no cost over the Internet offers the possibility of cheap volcano monitoring on a global scale. Herein we use an extensive, 690-scene AVHRR GAC dataset to observe volcanic activity in the Indonesian island arc between January 1996 and November 1997. Indonesia contains over 70 active volcanoes, with styles of activity during the observation period including active lava domes, lava flows, pyroclastic flows and hot crater lakes, many in close proximity to major centres of population. The detection potential of these and other phenomena in GAC data is assessed. Thermal anomalies were identified at ～18 volcanoes during the observation period, including lava flows at Anak Krakatau, persistent open-vent activity at Semeru and a previously unreported eruption at Sangeang Api volcano. Using these results, a classification scheme for night-time Indonesian GAC data is presented. Routine use of freely available high temporal resolution data such as AVHRR GAC could help elucidate cyclic activity at active volcanoes, which would contribute significantly to hazard mitigation in affected areas. Browse images of higher resolution data (e.g. SPOT) from the daily updated archives of the Centre for Remote Imaging, Sensing and Processing (CRISP) in Singapore also show potential as an aid to volcano monitoring in the region.     

基于工业热源区域识别的邯郸市热异常产品分析

利用目前空间分辨率、时间分辨率（1 d）最高的成熟热异常产品数据主动式热异常数据（ACF,NPP-VIIRS active fire/hotspot data）,结合基于长时序热异常数据支持下的工业热源区域识别模型,叠加地表覆盖类型数据,实现邯郸市不同类型热异常数据的识别与分析。(1)清洗邯郸市2012.1.20～2020.12.31年89 249个热异常点数据,得到2012～2020年间在营的81个工业热源区域,主要分布在京广线（G4高速）以西的丘陵地区,密集分布于涉县、武安、峰峰矿区,与邯郸市矿产资源的分布具有较好的一致性;2020年在营的工业热源与2013年相比,关停32个（42.67%）,热异常点数目明显减少的19个（25.33%）,新增5个企业;从企业类别上看,识别出的工业热源企业主要为钢铁及铸造类、煤化工及焦化、水泥厂等企业,分别占比达53.24%、28.16%和0.08%。(2)邯郸市2012～2020年历年的热异常点主要来源于工业热源,其工业热异常点历年平均占比为91.61%,2016年工业热源区域内热异常点占比最高,占比超过94.34%;邯郸市耕地地表覆盖中,有42....     

Updating geomorphic features of watersheds and their boundaries in hazardous areas using satellite synthetic aperture radar

Volcanic disasters can cause severe loss of human life and damage to property. The main damage is caused during an eruption and from subsequent erosion of deposited materials. Heavy rainfall in volcanic areas erodes volcanic deposits, mainly pyroclastic flows and ash fall deposits, which flow as lahar to the foothill of the mountain and cause drastic damage to economically important areas. This post-eruption disaster becomes complex due to the occurrence of stream captures and watershed breakouts that lead to devastating lahars. Continuous monitoring of such geomorphic and hydrologic changes is necessary to cope with changing hazard conditions. Therefore it is important to update the watershed boundaries in order to study current hazard conditions and develop mitigation plans for future disasters. Changes of geomorphic and watershed boundary have occurred in the Mayon Volcano in the Philippines mainly as a result of a major volcanic eruption of 1993, due to which mitigation structures were constructed and modified in the low lying areas. In this study interferometry was used to develop DEM from SAR data to delineate watershed boundaries. New lava flows, pyroclastic flows and lahar deposits in the watersheds were mapped using elevation changes, coherence and intensity derived from the SAR images. Updating geomorphic features of the watersheds and their boundaries using SAR provides a new weather independent alternative technique for monitoring the effect of volcanic activity.     

Hot-spot detection and characterization of strombolian activity from MODIS infrared data

Identifying and characterizing strombolian activity from space is a challenging task for satellite-based infrared systems. Stromboli volcano is a natural laboratory that offers a unique opportunity for refining thermal remote-sensing applications that involve transient phenomena and small to moderate hot-spots. A new simple and fast algorithm gave us the opportunity to revisit the MODIS-derived thermal output at Stromboli volcano over the last 13 years. The new algorithm includes both night-time and daytime data and shows high performance with the detection of small-amplitude thermal anomalies (<1 MW), as well as a low occurrence of false alerts (<4%). Here, we show that the statistical distribution of volcanic radiative power (VRP; in Watts) is consistent with the detection of variable activity regimes that we subdivided into five levels of thermal activity: Very Low (VRP < 1 MW), Low (1 MW < VRP < 10 MW), Moderate (10 MW < VRP < 100 MW), High (100 MW < VRP < 1000 MW), and Very High (VRP > 1000 MW). The ‘Low’ and ‘Moderate’ thermal levels are associated with strombolian activity and reflect fluctuations of the magma level within the conduit feeding the activity at the surface. The ‘High’ level of thermal output represents the bulk thermal emissions during periods of effusive activity. The highest level (‘Very High’) was reached only during the onset of flank eruptions (28 December 2002 and 27 February 2007). We found that the retrieved thermal regimes are in general agreement with the explosive levels evaluated at Stromboli since 2005, and their correlation has been shown to be dependent on the observed activity (i.e. eruption onset, lateral flank effusion, summit overflows, strombolian activity). Our results suggest that remotely sensed thermal data provide a reliable tool for monitoring volcanic activity at Stromboli volcano.     

Satellite observation of active carbonatite volcanism at Ol Doinyo Lengai,Tanzania

Natrocarbonatite lavas extruded by Ol Doinyo Lengai volcano, Tanzania, exhibit the lowest known magmatic eruption temperatures, ranging between 500 and 600 C. Nevertheless, as shown here, the near-infrared bands 5 and 7 of the Landsat Thematic Mapper (TM), and the mid-infrared channel 3 of the spaceborne Advanced Very High Resolution Radiometer (AVHRR) are able to detect thermal emission from active carbonatites. Laboratory-measured visible-to-near-infrared reflectance spectra of both silicate and carbonatite rocks from Ol Doinyo Lengai are used to infer spectral emissivities, enabling interpretation of satellite measurements. Given the remote location of this unique volcano, satellite remote sensing could play a valuable role in its future surveillance, and offers a potential means for distinguishing between silicate and carbonatite eruptions.     

Estimation of methane emission from West Siberian wetland by scaling technique between NOAA AVHRR and SPOT HRV

Wetlands are one of the most important ecosystems in the world and at the same time they are presumed to be a source of methane gas, which is one of the most important greenhouse gases. The West Siberian wetlands is the largest in the world and remote sensing techniques can play an important role for monitoring the wetland.High spatial resolution satellite data are effective for monitoring land cover type changes, but can't cover a wide area because of a narrow swath width. On the other hand, global scale data are indispensable in covering a large area, but are too coarse to get the detailed information due to the low spatial resolution. It is necessary to devise a method for the fusion of the data with different spatial resolutions for monitoring the scale-differed phenomena.In this paper, firstly, a SPOT HRV image near Plotnikovo mire was used to map four wetland ecosystems (birch forest, conifer forest, forested bog and open bog) supplemented by field observation. Then, spectral mixture analysis was performed between NOAA AVHRR and SPOT HRV data acquired on the same day.Secondly, field observations were scaled up with these different spatial resolution satellite data. Each of the wetland ecosystem coverage fraction at the sub-pixel level was provided by spectral mixture analysis. Field observation shows that the mean rate of CH₄ emission from forested bog and open bog averaged 21.1 and 233.1 (mg CH₄/m²/day), respectively. The methane emission from the area was estimated by multiplying these average methane emission rates and the fraction coverage in each AVHRR pixel.Finally, the total methane emission over AVHRR coverage was estimated to be 9.46 (10⁹ g CH₄/day) and the mean methane emission over AVHRR coverage was calculated as 59.3 (mg CH₄/m²/day). We could conclude that this mean value is within the probabilistic variability as compared with the airborne measurement results.     

Using NOAA/AVHRR data to determine regional net radiation and soil heat fluxes over the heterogeneous landscape of the Tibetan Plateau

In this study, a parameterization methodology based on NOAA/AVHRR (National Oceanic and Atmospheric Administration/Advanced Very High-Resolution Radiometer) data and field observations is described and tested for deriving the regional surface reflectance, surface temperature, net radiation flux and soil heat flux over a heterogeneous landscape. As a case study, the methodology was applied to the Tibetan Plateau area. Two scenes of NOAA/AVHRR data were used in this study. The derived results were also validated using the ‘ground truth’. The results show that reasonable regional distribution of surface variables (surface reflectance and surface temperature), net radiation flux and soil heat flux over the heterogeneous landscape of the Tibetan Plateau can be obtained by using this methodology. Further improvement of the methodology was also discussed.     

Remote Sensing Letters

The measurement of ground heat flux is required for many applications. Advanced Very High Resolution Radiometer (AVHRR) data are used within this study, the temporal resolution providing several overpasses throughout a single diurnal cycle at a suitable spatial and radiometric resolution. The technique of thermal inertia mapping by airborne and satellite-borne sensors has opened a new field of quantitative thermal property interpretation from thermal infrared remote sensing surveys. The algorithms adopted to calculate the ground heat flux were based on the second-order approximation thermal inertia model (SoA-TI model) of Xue and Cracknell. Not only the amplitude of the surface temperature wave but also the phase information of the surface temperature change are used. The approach is demonstrated by using some AVHRR data from France.