Dr Fred Prata, MIA-VITA team member,
Climate and Atmosphere Department, NILU, Kjeller, Norway
During February 2011 a small team of scientists led by Dr Fred Prata conducted some field trials of two novel ground-based imaging cameras on the slopes of the smoldering Merapi volcano. The cameras were developed at the Norwegian Institute for Air Research (NILU) for monitoring volcanic emissions remotely from distances of up to 10 km. Figure 1 shows the setup of the cameras at three measurement sites near Merapi.
Figure 1. Observation locations for the imaging cameras.
One aim of this work was to test the efficacy of using remote sensing equipment to monitor and quantify emissions for hazard mitigation.
During the field work, BPPTK scientists supported the MIA-VITA team, assisted in acquiring data and provided a guided tour of the devastation caused by the pyroclastic flows and lahars, that still remain as a threat to the safety of the people living near the slopes of Merapi. Figure 2 shows some examples.
Figure2. Upper-left: From left:CholikNoer (BPPTK), Jessie Kandlbauer (U. of Bristol), Andrew Prata (Bureau of Meterology, Australia), HanikHumaida (BPPTK), Chris Newhall (EOC, U. of Singapore), Steve Sparks (U. of Bristol), and Fred Prata (NILU), studying deposits on one of the pyroclastic flows. Upper right: Bent-over trees. Lower left: Landscape carved by a pyroclastic flow. Lower right: School house destroyed in Gendol village.
The NicAIR Infrared Imaging camera
The NicAIR camera is a fast-sampling, multi-channel imaging camera that can operate day or night by measuring passive infrared radiation from particulate and gaseous emissions. Processing the imagery allows estimates of the mass loading (g m-2) and, in the case of particulates, measurements of the effective particle radius of fine ash particles (1-16 µm radii).
Figure 3. Series of images obtained from the NicAIR camera. The bottom left image shows an SO2 retrieval (highest values coloured red) and can be compared with the visible image (bottom right).
NicAIR was setup at the top of the tower at the Kaliurang Observatory to monitor emissions from Merapi. The instruments are automated and continuous measurements were made as they were mounted at the top of the Kaliurang tower (see Fig. 1). An advantage of this setup is that the data can be relayed to a computer screen and images can be displayed in real-time to an observer in an office and at a safe distance from the volcano. Figure 4 shows an example of the kind of imagery that can be obtained from the cameras.
Figure 4. Temperature image from the NicAIR camera, showing an SO2 emission cloud near the summit of Merapi volcano. Further processing of these data will provide estimates of the emission rate and total SO2 mass emitted.
A graticule can also be overlaid onto the image (see Fig. 4) so that a measurement of the height of an eruption plume can be made. This is important information for assessing the severity of an eruption and also for forecasting the movement of volcanic ash and SO2, for example to provide warnings of aviation hazards. As the imagery can be obtained at night as well as day and as the sampling rate is high (~1 Hz), the data can be used as a warning system. The data can also be used to validate satellite measurements. Satellite instruments can also measure ash mass loadings and SO2 amounts. Figure 5 illustrates an ash mass loading map determined from the MTSAT in geosynchronous orbit and able to monitor Indonesian volcanoes at hourly time intervals.
Figure 5. Ash mass loading determined from the MTSAT for an eruption from Merapi at 05:30UT on 8 November 2010.
Figure 6. Height estimation from NicAIR at Karymsky volcano, Kamchatka.
The UV- EnviCam system
The second camera operates in the ultra-violet part of the spectrum and uses filters tuned to the strong absorption band of the SO2 molecule around 290-310 nm.
Figure 7. The EnviCam UV imaging camera monitoring SO2 emissions from Merapi.
This camera, EnviCam, requires sunlight and can sample at 1 Hz thus providing dynamic information of SO2 emissions. A unique feature of EnviCam is the incorporation of a high spectral resolution spectrometer that allows on site calibration of the measurements and the ability to remove extraneous effects due to clouds and other unwanted scattering effects.
The instruments operated well from distances up to 10 km and showed great potential for safe monitoring of volcanic emissions. The data from the cameras are currently being processed, but an example image acquired at Turrialba volcano in January 2011 is shown in Figure 8.
Figure 8. SO2 emissions from Turrialba volcano, Costa Rica on 18 January 2011, measured using the UV EnviCam system.
We are indebted to the scientists of the BPPTK (Balai Penyelidikan dan Pengembangan Teknologi Kegunungapian) the volcanological centre in Yogyokarta that is directly responsible for monitoring Merapi volcano. We made contact with a few of the scientists working there and also got a better understanding of the events that took place. Cholik Noer (firstname.lastname@example.org) and Hanik Humaida (email@example.com) were kind enough to allow us use of their observation tower and station and to also to provide their expert knowledge of Merapi volcano. Chris Newhall and Steve Sparks are thanked for assistance with the filed work and logistics. Andrew Prata, Monash University (honours student) assisted on the field campaign and helped with the data acquisition and processing.