MIROVA. UNIVERSIT degli studi di Firenze e Torino

MIROVA

Middle InfraRed Observation of Volcanic Activity is a near real time volcanic hot-spot detection system based on the analysis of MODIS ( Moderate Resolution Imaging Spectroradiometer) data . In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity.

Main Features

  • Automated thermal monitoring of the most active volcanoes on earth provided in near real time (within 1 to 4 hours from the satellite overpass);
  • High sensibility of the hot spot detection system for small thermal anomalies (~1 MW);
  • Quick overview of the latest thermal images;
  • Updated Volcanic Radiative Power (VRP) time-series in logarithmic and normal scale;
  • Thermal outputsubdivided into 5 distinct levels based on VRP. Quick comparison of the observed thermal output of different volcanoes;
  • Last thermal map image of each volcano available for Google Earth overlapping;
  • Possibility to add any new target volcanoes in near real time observation, in any area of the globe (on request in few hours);
The main goal of MIROVA system is to provide near real time observations of volcanic activity and to update a multi-year database of infrared satellite data at several active volcanoes. Please read here about the use of the data provided in this website

Near Real Time

MIROVA NRT (Near Real-Time) is based on the automated analysis of MODIS data distributed by the LANCE-MODIS data system. Whereas the standard MODIS forward processing delivers Aqua and Terra images within 7-8 hours of real time, LANCE-MODIS allows for the cration of MIROVA NRT within 1-4 hours from the satellite overpass.

MODIS

MODIS (or Moderate Resolution Imaging Spectroradiometer) is a key instrument aboard theTerra (EOS AM) and Aqua (EOS PM) satellites.

Terra's orbit around the Earth is timed so that it passes from north to south across the equator in the morning, while Aqua passes south to north over the equator in the afternoon. Terra MODIS and Aqua MODIS are imaging the entire Earth's surface every 1 to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths (see below).

The MODIS instrument provides high radiometric sensitivity (12 bit) in 36 spectral bands ranging in wavelength from 0.4 m to 14.4 m. The responses are custom tailored to the individual needs of the user community and provide exceptionally low out-of-band response.

Two bands are imaged at a nominal resolution of 250 m at nadir, with five bands at 500 m, and the remaining 29 bands at 1 km. A &plusminus;55-degree scanning pattern at the EOS orbit of 705 km achieves a 2,330-km swath and provides global coverage every one to two days. Specifications (from MODIS Technical page) Orbit: 705 km, 10:30 a.m. descending node (Terra) or 1:30 p.m. ascending node (Aqua), sun-synchronous, near-polar, circular Scan Rate: 20.3 rpm, cross track Swath Dimensions: 2330 km (cross track) by 10 km (along track at nadir) Telescope: 17.78 cm diam. off-axis, afocal (collimated), with intermediate field stop Size: 1.0 x 1.6 x 1.0 m Weight: 228.7 kg Power: 162.5 W (single orbit average) Data Rate: 10.6 Mbps (peak daytime); 6.1 Mbps (orbital average) Quantization: 12 bits Spatial Resolution: 250 m (bands 1-2) 500 m (bands 3-7) 1000 m (bands 8-36) Design Life: 6 years

Primary Use Band Bandwidth1 Spectral
Radiance2
Required
SNR3
Land/Cloud/Aerosols
Boundaries
1 620 - 670 21.8 128
2 841 - 876 24.7 201
Land/Cloud/Aerosols
Properties
3 459 - 479 35.3 243
4 545 - 565 29.0 228
5 1230 - 1250 5.4 74
6 1628 - 1652 7.3 275
7 2105 - 2155 1.0 110
Ocean Color/
Phytoplankton/
Biogeochemistry
8 405 - 420 44.9 880
9 438 - 448 41.9 838
10 483 - 493 32.1 802
11 526 - 536 27.9 754
12 546 - 556 21.0 750
13 662 - 672 9.5 910
14 673 - 683 8.7 1087
15 743 - 753 10.2 586
16 862 - 877 6.2 516
Atmospheric
Water Vapor
17 890 - 920 10.0 167
18 931 - 941 3.6 57
19 915 - 965 15.0 250

Primary Use Band Bandwidth1 Spectral
Radiance2
Required
NE[delta]T(K)4
Surface/Cloud
Temperature
20 3.660 - 3.840 0.45(250K) 0.05
21 3.929 - 3.989 2.38(335K) 2.00
22 3.929 - 3.989 0.67(250K) 0.07
23 4.020 - 4.080 0.79(250K) 0.07
Atmospheric
Temperature
24 4.433 - 4.498 0.17(250K) 0.25
25 4.482 - 4.549 0.59(275K) 0.25
Cirrus Clouds
Water Vapor
26 1.360 - 1.390 6.00 150(SNR)
27 6.535 - 6.895 1.16(240K) 0.25
28 7.175 - 7.475 2.18(250K) 0.25
Cloud Properties 29 8.400 - 8.700 9.58(250K) 0.05
Ozone 30 9.580 - 9.880 3.69(250K) 0.25
Surface/Cloud
Temperature
31 10.780 - 11.280 9.55(250K) 0.05
32 11.770 - 12.270 8.94(250K) 0.05
Cloud Top
Altitude
33 13.185 - 13.485 4.52(260K) 0.25
34 13.485 - 13.785 3.76(250K) 0.25
35 13.785 - 14.085 3.11(240K) 0.25
36 s14.085 - 14.385 2.08(220K) 0.35

1Bands 1 to 19 are in nm; Bands 20 to 36 are in m
2Spectral Radiance values are (W/m2-m-sr)
3SNR = Signal-to-noise ratio
4NE(delta)T = Noise-equivalent temperature difference

Note:Performance goal is 30-40% better than required

Middle InfraRed Radiation

The ElectroMagnetic (EM) radiation with wavelengths longer that those of visible light is called InfraRed radiation (IR). This range of emissions spans from 0.74 m to 250 m and includes the thermal radiation emitted by the volcanic products as well as by objects near room temperature. A commonly used subdivision scheme distinguishes the infrared electromagnetic spectrum into 5 regions as showed in the Table below.

Near-InfraRed NIR from 0.75 to 1.4 m
Short-Wavelength InfraRed SWIR from 1.4 to 3 m
Middle Wavelength InfraRed MWIR from 3 to 8 m also called Middle InfraRed (MIR)
Long-Wavelength InfraRed LWIR from 8 to 15 m also called Thermal InfraRed (TIR)
Far InfraRed FIR from 15 to 1000 m

Table 1 - Subdivision scheme of infread electromagnetic spectrum.

The most useful regions for observing the thermal signature of volcanic bodies are those between 1.4 and 12 m (SWIR, MIR and TIR). However, the thermal emission from an object is attenuated by the atmospher resulting from absorption by gases and scattering by particles.

This attenuation is wavelength dependent and may be so high that the radiation emitted from an object on the earth's surface is absorbed or scattered to a degree that is not detectable by satellite. There are, nonetheless, certain parts of the infrared spectrum for which the atmospheric attenuation is low ("atmospheric windows", see Fig. 1)

Fig. 1 - Typical transmission pattern of the atmosphere. Black arrows mark the wavelengths with increased adsorption through atmospheric gases. The NIR,SWIR,MIR and TIR regions of EM are marked by the different background colors. The shaded gray bars correspond to the MODIS infrared channels.

The Middle InfraRed region (MIR), betwenn 3.5 and 4 m, shows the lowest attenuation levels. MIROVA focuses on these data to detect and analyze thermal radiation emitted from volcanic sources.

Volcanic Radiative Power

The Volcanic Radiative Power (VRP) is a measurement of the heat radiated by the volcanic activity at the time of a satellite acquisition (Coppola et al., 2013).

The VRP is calculated in Watts (W) and represents a combined measurement of the area of the volcanic emitter and its effective radiating temperature. MIROVA calculates the Volcanic Radiative Power (VRP) by using the "MIR method", an approach which was initially introduced by in order to estimate the heat radiated by active fires, using satellite data (Wooster et al., 2003).

This approach (also known as Middle InfraRed method) relies on the fact that whenever an hot emitter has an "effective radiating temperature" higher than 600 K, the "excess" of radiance detected in the MIR region (DLMIR), can be linearly related to the the radiative power (30%). Hence, for any individual hot-spot contaminated MODIS pixels, MIROVA calculates the VRP as: VRP = 18.9 x APIX x DLMIR where 18.9 is a best-fit regression coefficient (see Wooster et al., 2003), APIX is the pixel size (1 km2 for the MODIS pixels) and DLMIR is the "above background" MIR radiance of the pixel. When a hot-spot is detected in more than one pixel, the total VRP is calculated as the sum of all pixels detecting a hot-spot.

References Wooster, MJ, Zhukov, B, Oertel, D (2003). Fire radiative energy for quantitative study of biomass burning: derivation from the BIRD experimental satellite and comparison to MODIS fire products. REMOTE SENSING OF ENVIRONMENT, 86(1), 83-107.

Coppola, D., Laiolo, M., Piscopo, D., Cigolini, C. (2009). Rheological control on the radiant density of active lava flows and domes. J. Volcanol. Geotherm. Res. 249: p. 39-48..