本多 嘉明

In December 2019, a new activity started at Nishinoshima volcano in the southern part of the Izu–Ogasawara arc, Japan. This is now referred to as Episode 4 of a series of activities that began in 2013. We analyzed the eruption sequence, including erupted volume and effusion rate, based on combined observations of thermal anomalies by Himawari-8 and topographic changes by ALOS-2. The total eruption volume during Episode 4 was ~ 132 × 106 m3, and the average effusion rate over the entire period was 0.51 × 106 m3 day−1 (5.9 m3 s−1), which was two to three times higher than that of Episode 1. Episode 4 had three stages. In Stage 1, effusive activity was dominant, and most of the lava erupted from a northeast vent at the foot of the pyroclastic cone to cover the northern half of the island. The average effusion rate was estimated to be 0.46 × 106 m3 day−1 (5.3 m3 s−1). In Stage 2, an intensive lava fountain with a high discharge rate developed, and it increased the size of the pyroclastic cone rapidly. The effusion rate temporarily reached 2.6 × 106 m3 day−1 (30 m3 s−1). Pyroclastic rocks accounted for 45–88% of the total erupted volume in this stage. Lava flows with rafted cone material were generated, and those possibly caused by intensive spatter falls on the slope were also formed. These lavas flowed down the southern half of the island. In Stage 3, continuous phreatomagmatic eruptions released ash and spread it over a wide area. The high effusion rate and the drastic change in the activity style in Episode 4 can be explained by deep volatile-rich magma being supplied to a shallower magma chamber prior to Episode 4. When the volatile-rich magma reached a shallow part of the conduit in Stage 2, fragmentation occurred due to rapid volume expansion to eject large amounts of magma and form the intensive lava fountain. Observations by satellite-borne ultraviolet–visible image sensors detected a rapid increase in SO2 emissions in response to the intensive lava-fountain activity. The less-differentiated nature of the ash fragments collected during Stage 2 may reflect the composition of the volatile-rich magma. Large-scale discolored-seawater areas appeared during the late period of Stage 1, which may have been caused by ascent of the volatile-rich magma. Graphical Abstract: [Figure not available: see fulltext.].

Miyakejima volcano experienced its latest eruption in 2000 with the summit subsidence, and the next event is expected in the near future. An aeromagnetic survey in Miyakejima was conducted in March 2021 in order to investigate the current state of its magnetization structure to identify the potential for another eruption and, thus, mitigate volcanic disaster. The survey flight was conducted using an uncrewed aerial vehicle (UAV), a multirotor drone, to deploy a scalar magnetometer. After processing geomagnetic field data from this survey, in combination with data from previous surveys conducted by using another UAV, an uncrewed helicopter, the average magnetization intensity was determined to be 12.4 A/m. Further, the surrounding area of the crater was relatively highly magnetized; however, the crater rim had a low magnetization intensity. Temporal variation was detected between 2014 and 2021 and dominated the central part of the observation area. Decreased magnetization intensity was identified beneath the caldera, which may become recently demagnetized due to heat supply traveling through fractures in the impermeable layer from the deep heat reservoir.

We conducted a high-resolution aeromagnetic survey using an autonomously driven uncrewed helicopter that flew as low as several tens of meters above the ground along precise flight tracks with 1 m accuracy. The geomagnetic total intensity was measured by a total intensity magnetometer suspended beneath the helicopter at a ~ 50 m or less flight spacing over the entire caldera of Mt. Mihara, located on Izu-Oshima Island, Japan. From the observed geomagnetic data, we estimated high-resolution subsurface magnetization intensity. A high average magnetization intensity of 13.5 A/m was obtained for the entire caldera. The distribution of the magnetization intensity was not only consistent with the results of conventional airborne surveys, but it also had a high spatial resolution of less than 100 m. Highly magnetized areas were observed along the NW–SE lines that intersected the summit pit crater, Crater A, which is consistent with the principal stress direction of Izu-Oshima Island. These highly magnetized areas might be solidified magma that did not reach the surface during past eruptions. A large and deep-rooted weakly magnetized area was found just outside of the NE side of the central cone, which corresponds to the location of Fissure B, and the conduit must have been demagnetized at the previous event. Other weakly magnetized areas were also observed at the N, E, and SW sides around the pit crater. These regions correspond to the location of fumaroles in the crater. The high-resolution subsurface magnetization imaged by the autonomous uncrewed helicopter will be helpful for the mitigation of future eruption damage by enabling the assessment of potential fissure eruption areas.

無人飛翔体は被災するおそれのある危険地域へ人が入域することなく各種測定を実施することを可能とするため，今世紀に入ってから特に着目され，現在までに多様な火山観測項目に利用されている。その中で自律型無人ヘリコプターは，高い位置精度で事前にプログラミングした航路に沿ってフライトすることが可能になるため，たとえば対地高度や測線間隔を一定に保つなど理想的な測線を組むことが可能になることに加えて，時間間隔をおいて同一の測線に沿って繰り返し観測を実施することで同一地点での観測量の時間変化を捉えることが可能となる。そのため，火山体での空中磁気測量を自律型無人ヘリコプターを用いて実施することにより，複雑な地形上でも均質な空間解像度の磁場測定を可能にし，また，複数回繰り返し行うことで噴火準備過程などの火山活動に伴う磁場の長期的な時間変化を検出することができる。伊豆大島三原山では対地高度および測線間隔を平均50 mとした稠密な空中磁気測量を実施し，過去に噴出せず地下で固化したと考えられる高磁化の領域が中央火口丘周辺に確認された。霧島新燃岳では2011年噴火活動以降繰り返し空中磁気測量を実施することにより，火口内に滞留した溶岩が冷却帯磁により時間を追って磁化を獲得していく様子を明瞭に検出することができた。ここ数年は電動式マルチコプターの開発およびその利用がめざましく，今後も無人飛翔体による火山観測のさらなる発展が期待される。

Kusatsu-Shirane volcano is one of the active volcanoes in Japan. Phreatic explosions occurred in Mt. Shirane in 1983 and most recently, in 2018, in Mt. Motoshirane. Information on the subsurface structure is crucial for understanding the activity of volcanoes with well-developed hydrothermal systems where phreatic eruptions occur. Here, we report aeromagnetic surveys conducted at low altitudes using an unmanned helicopter. The survey aimed to obtain magnetic data at a high spatial resolution to map the magnetic anomaly and infer the magnetization intensity distribution in the region immediately after the 2018 Mt. Motoshirane eruption. The helicopter used in the survey was YAMAHA FAZER R G2, an autonomously driven model which can fly along a precisely programmed course. The flight height above the ground and a measurement line spacing were set to similar to 150 m and similar to 100 m, respectively, and the total flight distance was 191 km. The measured geomagnetic total intensity was found to vary by similar to 1000 nT peak-to-peak. The estimated magnetization intensity derived from measured data showed a 100 m thick magnetized surface layer with normal polarity, composed of volcanic deposits of recent activities. Underneath, a reverse-polarity magnetization was found, probably corresponding to the Takai lava flow in the Early Quaternary period (similar to 1 Ma) mapped in the region. Our results demonstrate the cost-effectiveness and accuracy of using drone magnetometers for mapping the rugged terrain of volcanoes.

To validate and to improve ecological products obtained from satellites, such as a leaf area index (LAI), above-ground biomass (AGB), and a fraction of photosynthetically active radiation (fAPAR), in-situ accurate data are indispensable. They must be not a single point-data but an areal data representing the satellite footprint. Their accuracy needs to be much higher than the required accuracy for the satellite products. The quantitative assessment of their error is necessary for evaluating the satellite products' error from the discrepancy between the satellite products and the in-situ data. However, such data had not been available. In particular, there had been few data of LAI in a sparse evergreen needle-leaved forest, because of difficulty of accuracy control of in-situ observation in such a forest. To overcome the difficulty and to obtain the representative LAI, we made an allometric equation to estimate the leaf mass of Picea glehnii in northern Hokkaido. We report the allometric equations of leaf mass and AGB of P. glehnii, its leaf mass per area (LMA), its leaf life span, its leaf distribution, its crown shapes, its wood specific gravity, and tree locations. We also report LAI, AGB, and fAPAR within the 500 m x 500 m area, which is the footprint scale of the Global Change Observation Mission-Climate satellite, in a pure and sparse forest of P. glehnii in northern Hokkaido. These precise data are useful for validation of other satellite data, especially with higher spatial resolution, and forest structure modeling.

The GCOM-C (SHIKISAI) satellite was developed to understand the mechanisms of global climate change. The second-generation global imager (SGLI) onboard GCOM-C is an optical sensor observing wavelengths from 380 nm to 12.0 mu m in 19 bands. One of the notable features is that the resolution of the 1.63, 10.8, and 12.0 mu m bands is 250 m, with an observation frequency of 2-3 days. To investigate the effective use and potential of the 250 m resolution of these SGLI bands in the study of eruptive activities, we analyzed four practical cases. As an example of large-scale effusive activity, we studied the 2018 Kilauea eruption. By analyzing the series of 10.8 mu m band images using cumulative thermal anomaly maps, we could observe that the lava effused on the lower East Rift Zone, initially flowed down the southern slope to the sea, and then moved eastward. As an example of lava dome growth and generation of associated pyroclastic flows, the activity at Sheveluch between December 2018 and December 2019 was analyzed. The 1.63 and 10.8 mu m bands were shown to be suitable for observing growth of the lava dome and occurrence of pyroclastic flows, respectively. We found that the pyroclastic flows occurred during periods of rapid lava dome expansion. For the study of an active crater lake, the activity of Ijen during 2019 was analyzed. The lake temperature was found to rise rapidly in mid-May and reach 38 degrees C in mid-June. We also analyzed the intermittent activities of small-scale vulcanian eruptions at Sakurajima in 2019. The 1.63 mu m band was useful for detecting activities that are associated with vulcanian eruptions. Analytical results for these case studies demonstrated that the GCOM-C SGLI images are beneficial for observing various aspects of volcanic activity, and their real-time use may contribute to reducing eruption-related disasters.

<p>In this paper, we present an algorithm for estimating terrestrial albedo for the product of Global Change Observation Mission-Climate (GCOM-C)/Second generation Global Imager (SGLI), that was launched in Dec. 2017 by Japan Aerospace Exploration Agency (JAXA), Japan. The algorithm is composed of spectral albedo estimation, narrowband-to-broadband albedo conversion and multi-regression model estimation so that only a single-day reflectance observation is available. In estimating spectral albedo, we derives coefficients of kernel-driven bidirectional reflectance distribution function (BRDF) model. The experiments by using in-situ data of bare soil and deciduous broadleaf forests show that the proposed method have potential to estimating albedos with acceptable accuracy of the root mean square of errors (RMSE) of 2.2×10^-2 and 4.3×10^-2.</p>

草津白根火山は,2つの主な山体から成る:1つは北部で白根山であり,もう1つは南部の本白根である。火山噴火の最近の活動は,主に白根山での噴火として特徴付けられ,最後の噴火は1983年に生じ,いくつかの火山地震がこれまでに検出された。一方,本白根山は,約1,500年間,噴火活動がなく,一方,それは,本白根山の東側に位置する,万代鉱,湯畑,および他の温泉で,約30,000l/minの大量の熱水を排出する。小さな噴火は,2018年1月23日に本白根山の鏡池と鏡池北の火砕円錐で生じ,一方,2014年より白根山観測点で火山性地震や地磁気全磁力強度の変化が記録されていたので白根山での更なる噴火活動が懸念された。噴火後,無人ヘリコプタを用いて,3月,6月,および10月に両山体の上空で空中磁気調査を行った。また,2014年に有人ヘリによるMLITによって取得したデータを用い,噴火前後の磁場の変化を取得した。地磁気変化の3つの顕著な特徴を見出した。1)消磁異常は白根-本白根地域にあり,その空間規模は数kmである。2)白根山の湯釜火口の東に約数百m規模の小さな異常変化がある。この異常の位置は最近の火山噴火の震源に対応し,熱水系に関係する可能性がある。3)鏡池クレータの周りで,小型で不均一な地磁気変化を見出した。この変化は熱起源ではなく,2018噴火の噴火活動による地形変化によるものであろう。このように,この噴火は,最初に1)における深部の大規模な熱あるいはマグマ活動によって引き起こされたが,クレータの表面下に検出される顕著な異常はなかったので,予想外の水蒸気噴火となった。(翻訳著者抄録)

Japan Aerospace Exploration Agency (JAXA) had launched new Earth observation satellite GCOM-C in the end of 2017. The core sensor of GCOM-C, Second Generation Global Imager (SGLI) has a set of along track slant viewing Visible and Near Infrared Radiometer (VNR). These multi-angular views aim to detect the structural information from vegetation canopy, especially forest canopy, for estimating productivity of the vegetation. SGLI Land science team has been developing the algorithm for Above Ground Biomass, Vegetation Index, Shadow Index, etc.We developed the ground observation method using Unmanned Aerial Vehicle (UAV) in order to contribute the algorithm development and its validation. Mainly, multiangular spectral observation method and simple BRF model have been developed for estimating slant view response of forest canopy. The BRF model developed by using multiangular measurement has been able to obtain structural information from canopy. In addition, we have conducted some observation campaigns on typical forest in Japan in collaboration with other science team experienced with vegetation phenology and carbon flux measurement. Primary results of these observations are also be demonstrated.

To validate terrestrial ecological products of the Global Change Observation Mission-Climate (GCOM-C) satellite, a large-scale ecological observation project "JAXA Super Sites 500" was initiated. The project's purpose is to obtain the representative leaf area index (LAI), above-ground biomass (AGB), and fraction of absorbed PAR (fAPAR) in the satellite footprint scale. This study aimed to determine the appropriate observation methods in the satellite scale for the target land-cover types such as a deciduous broad-leaved forest, evergreen/deciduous needle-leaved forests, and a grassland. As a result of the comparative observations, a combination method using litter-traps and LAI-2200 was adopted as the LAI observation in a forest, a tree census method was adopted as the AGB observation in a forest, and a clipping method was adopted as the AGB and LAI observations in a grassland. LAI, AGB, and fAPAR were observed and were used to validate the GCOM-C terrestrial ecological products.

After publication of this article (Kaneko et al. 2018), it is noticed there is an error in Fig. 3b; the lower 2.3-µm band image is mistakenly removed. The correct Fig. 3 is given below.

Forest disturbance by heavy snow seriously affects ecosystem functions and provision of ecosystem services. To evaluate the spatial distribution of this disturbance over large areas, it is necessary to develop a flexible, inexpensive, and generalizable method based on remote sensing. Here, we examined the ability of an unmanned drone to detect the disturbance caused by heavy snow in a Japanese cedar (Cryptomeria japonica) forest, which is a typical landscape species in Japan's mountainous areas. We obtained aerial photographs in late October 2016 using the drone in a research plot where many individuals were damaged by moist, heavy snow in mid-December 2014. The forest disturbance rate was estimated by visually inspecting the structure from motion (SfM) point clouds generated from the drone's aerial photographs. We detected 90 to 96% of healthy individuals, but many tilted trees and trees with broken stems but an intact canopy were misidentified as healthy individuals. The estimated forest disturbance rate (33%) obtained from the SfM point clouds coincided well with the actual forest disturbance rate (35%) obtained from tree surveys. Consequently, this approach can potentially be used to detect narrow and patchy disturbances in Japanese cedar forest, although further observations at multiple points will be required to develop the accuracy of this approach.

無人車両を用いたアクティブ火山の観測は,様々な観点から非常に重要である。科学的観点からは,彼/彼女の生命を危険にさらすことなく,活発なベントの近傍において観察を行うことが重要である。火山災害軽減の観点から,既存のモニタリングステーションが火山の強い活動によって損傷を受けるとき,損傷センサーのための再設置と回復技術は,活発な火山のまわりの観測ネットワークを維持するために不可欠である。無人車両を用いた火山監視センサの設置は,人間の生命のリスクを費やすことなく,損傷したステーションを回復する最も有望な方法である。2005年に,リスクフリー火山観測ツールを開発するプロジェクトを開始した。このプロジェクトでは,ヤマハ発動機社製の無人自律ヘリコプタRMAX-G1を採用した。セシウム磁力計によるこのヘリコプタを用いた航空磁気探査システムの開発に,最初の数年間を費やした。このシステムは徐々に改良され,伊豆大島,桜島,霧島島,口永良部島,その他で用いられた。活火山での空中磁気探査は,これらのターゲット火山の磁化構造を高い空間分解能で明らかにした。また,地震やGPS観測モジュールのような直接接地接触を必要とする観測モジュールの開発を開始した。著者らは,ヘリコプタの下に取り付けたウインチを開発し始め,活火山火口近くのターゲット領域にセンサを設置するのに用いた。観測モジュールは軽量,小型,および太陽電池式でなければならない。著者らは,2009年以降桜島山頂域で地震観測をまた,2011年以降GPS観測を維持してきた。2014年と2015年に噴火した南九州の口永良部島では,これまでに開発されたUAVベースの観測技術を採用した。山頂エリアで損傷した地震ネットワークを回復した。また,航空磁気調査,可視および赤外線画像,および火山ガスサンプリングを含む多重パラメータ観測も行った。また,小笠原西方130knの父島に新たに形成された西島火山島の観測のために観測システムを適用した。(翻訳著者抄録)

静止衛星による地球観測の経緯,現状,将来展望を述べた。日本の静止衛星は,1977年のGMS初号機以来,現行の「ひまわり8号」が2016年打ち上げの9号とともに相互にバックアップ観測体制を確立し2029年まで継続予定である。静止衛星による全球観測は現在6機程度の静止気象衛星によりカバーすることにより実現されている。今後は高性能イメージャによる観測継続と併せて,赤外ハイパースペクトラル・サウンダおよび雷検知装置の次期静止衛星での実現を目指している。

For monitoring of global environmental change, the Japan Aerospace Exploration Agency (JAXA) has made a new plan of Global Change Observation Mission (GCOM). SGLI (Second Generation GLI) onboard GCOM-C (Climate) satellite, which is one of this mission, provides an optical sensor from Near-UV to TIR. Characteristic specifications of SGLI are as follows 1) 250m resolutions over land and area along the shore, 2) Three directional polarization observation (red and NIR), and 3) 500m resolutions temperature over land and area along shore. The final check of the sensor system has been completed in 2016. The final check of the entire satellite system will be completed in the first half of 2017. The launch of GCOM - C is scheduled for the second half of 2017. These characteristics are useful in many fields of social benefits. In addition, 51 products will be made by mainly 35 principal investigators. There are 14 land products of SGLI (standard products are 9, and research products are 5). Already the Land team completed most of the algorithm and have created a product validation plan. Currently land team are improving the performance of the algorithm and preparing for verification. These activities are reported in this paper.

Five programs, i.e. ASTER, GOSAT, GCOM-W1, GPM and ALOS-2 are going on in Japanese Earth Observation programs. ASTER has lost its short wave infrared channels. AMSR-E stopped its operation, but it started its operation from Sep. 2012 with slow rotation speed. It finally stopped on December 2015. GCOM-W1 was launched on 18, May, 2012 and is operating well as well as GOSAT. ALOS (Advanced Land Observing Satellite) was successfully launched on 24th Jan. 2006. ALOS carries three instruments, i.e., PRISM (Panchromatic Remote Sensing Instrument for Stereo Mapping), AVNIR-2 (Advanced Visible and Near Infrared Radiometer), and PALSAR (Phased Array L band Synthetic Aperture Radar). Unfortunately, ALOS has stopped its operation on 22nd, April, 2011 by power loss. GOSAT (Greenhouse Gas Observation Satellite) was successfully launched on 29, January, 2009. GOSAT carries 2 instruments, i.e. a green house gas sensor (TANSO-FTS) and a cloud/aerosol imager (TANSO-CAI). The main sensor is a Fourier transform spectrometer (FTS) and covers 0.76 to 15 mu m region with 0.2 to 0.5 cm(-1) resolution. SMILES (Superconducting Millimeter wave Emission Spectrometer) was launched on September 2009 to ISS and started the observation, but stopped its operation on April 2010. GPM (Global Precipitation Mission) core satellite was launched on Feb. 2014. GPM is a joint project with NASA and carries two instruments. JAXA has developed DPR (Dual frequency Precipitation Radar) which is a follow on of PR on TRMM. ALOS F/O satellites are divided into two satellites, i.e. SAR and optical satellites. The first one of ALOS F/O is called ALOS 2 and carries L-band SAR. It was launched on May 2014. JAXA is planning to launch follow on of optical sensors. It is now called Advanced Optical Satellite and the planned launch date is fiscal 2019. Other future satellites are GCOM-C1 (ADEOS-2 follow on), GOSAT-2 and EarthCare. GCOM-C1 will be launched on 2017 and GOSAT-2 will be launched on fiscal 2018. Another project is EarthCare. It is a joint project with ESA and JAXA is going to provide CPR (Cloud Profiling Radar). EarthCare will be launched on 2019.