Luke P. Flynn

The MODIS 2.1-/spl mu/m channel-correlation with visible reflectance for use in remote sensing of aerosol

A new technique for remote sensing of aerosol over the land and for atmospheric correction of Earth imagery is developed. It is based on detection of dark surface targets in the blue and red channels, as in previous methods, but uses the 2.1 /spl mu/m channel, instead of the 3.75 /spl mu/m for their detection. A 2.1-/spl mu/m channel is present on ADEOS OCTS and GLI and planned on EOS-MODIS and EOSP, and a similar 2.2-/spl mu/m channel is present on Landsat TM. The advantage of the 2.1-/spl mu/m channel over the 3.75-/spl mu/m channel is that it is not affected by emitted radiation. The 2.1-/spl mu/m channel is transparent to most aerosol types (except dust) and therefore can be used to detect dark surface targets. Correlation between the surface reflection in the blue (0.49 /spl mu/m), red (0.66 /spl mu/m), and 2.1 /spl mu/m is established using atmospherically corrected Landsat TM and AVIRIS aircraft images collected over the Eastern United States, Maine, and California and spectral data obtained from the ground and light aircraft near San Diego, CA. Results from a variety of surface covers show that the surface reflectance at 0.49 /spl mu/m (/spl rho//sub 0.49/) and 0.66 /spl mu/m (/spl rho//sub 0.66/) can be predicted from that at 2.2 /spl mu/m (/spl rho//sub 2.2/) within /spl Delta//spl rho/=/spl plusmn/0.06 for /spl rho//sub 2.2//spl les/0.10, using /spl rho//sub 0.49/=/spl rho//sub 2.2//4 and /spl rho//sub 0.66/=/spl rho//sub 2.2//2. Error in surface reflectance of 0.006 corresponds to an error in remote sensing of aerosol optical thickness, /spl tau/, of /spl Delta//spl tau//spl sim//spl plusmn/0.06. These relationships were validated using spectral data taken close to the surface over vegetated areas in a different biome. This method expends application of dark targets for remote sensing of aerosol to brighter, nonforested vegetation. The higher reflection of the surface at 2.2 /spl mu/m than that of 3.75 /spl mu/m may even enable remote sensing of dust above surfaces with reflectivity /spl rho//sub 2.2/=0.15/spl plusmn/0.05. For this reflectivity range the dust radiative effect at 2.2 /spl mu/m is small, and the surface reflectance in the blue and red channels can be retrieved.

Potential global fire monitoring from EOS‐MODIS

The National Aeronautic and Space Administration (NASA) plans to launch the moderate resolution imaging spectroradiometer (MODIS) on the polarorbiting Earth Observation System (EOS) providing morning and evening global observations in 1999 and afternoon and night observations in 2000. These four MODIS daily fire observations will advance global fire monitoring with special 1 km resolution fire channels at 4 and 11 μm, with high saturation of about 450 and 400 K, respectively. MODIS data will also be used to monitor burn scars, vegetation type and condition, smoke aerosols, water vapor, and clouds for overall monitoring of the fire process and its effects on ecosystems, the atmosphere, and the climate. The MODIS fire science team is preparing algorithms that use the thermal signature to separate the fire signal from the background signal. A database of active fire products will be generated and archived at a 1 km resolution and summarized on a grid of 10 km and 0.5°, daily, 8 days, and monthly. It includes the fire occurrence and location, the rate of emission of thermal energy from the fire, and a rough estimate of the smoldering/flaming ratio. This information will be used in monitoring the spatial and temporal distribution of fires in different ecosystems, detecting changes in fire distribution and identifying new fire frontiers, wildfires, and changes in the frequency of the fires or their relative strength. We plan to combine the MODIS fire measurements with a detailed diurnal cycle of the fires from geostationary satellites. Sensitivity studies and analyses of aircraft and satellite data from the Yellowstone wildfire of 1988 and prescribed fires in the Smoke, Clouds, and Radiation (SCAR) aircraft field experiments are used to evaluate and validate the fire algorithms and to establish the relationship between the fire thermal properties, the rate of biomass consumption, and the emissions of aerosol and trace gases from fires.

Automated volcanic eruption detection using MODIS

Abstract The moderate resolution imaging spectroradiometer (MODIS) flown on-board NASAs first earth observing system (EOS) platform, Terra, offers complete global data coverage every 1–2 days at spatial resolutions of 250, 500, and 1000 m. Its ability to detect emitted radiation in the short (4 μm)- and long (12 μm)-wave infrared regions of the electromagnetic spectrum, combined with the excellent geolocation of the image pixels (∼200 m), makes it an ideal source of data for automatically detecting and monitoring high-temperature volcanic thermal anomalies. This paper describes the underlying principles of, and results obtained from, just such a system. Our algorithm interrogates the MODIS Level 1B data stream for evidence of high-temperature volcanic features. Once a hotspot has been identified, its details (location, emitted spectral radiance, satellite observational parameters) are written to an ASCII text file and transferred via file transfer protocol (FTP) to the Hawaii Institute of Geophysics and Planetology (HIGP), where the results are posted on the Internet ( http://modis.higp.hawaii.edu ). The global distribution of volcanic hotspots can be examined visually at a variety of scales using this website, which also allows easy access to the quantitative data contained in the ASCII files themselves. We outline how the algorithm has proven robust as a hotspot detection tool for a wide range of eruptive styles at both permanently and sporadically active volcanoes including Soufriere Hills (Montserrat), Popocatepetl (Mexico), Bezymianny (Russia), and Merapi (Java), amongst others. We also present case studies of how the system has allowed the onset, development, and cessation of discrete eruptive events to be monitored at Nyamuragira (Congo), Piton de la Fournaise (Reunion Island), and Shiveluch (Russia).

Effusion rate trends at Etna and Krafla and their implications for eruptive mechanisms

Abstract Using effusion rates obtained from ground- and satellite-based data we build a data set of 381 effusion rate measurements during effusive activity at Etna and Krafla between 1980 and 1999. This allows us to construct detailed effusion rate curves for six fissure-fed eruptions at Etna and Krafla and four summit-fed eruptions at Etna. These define two trends: Type I and II. Type I trends have effusion rates that rise rapidly to an initial peak, before declining more slowly, resulting in an exponential decrease in eruption rate and declining growth in cumulative volume. Type II trends are characterised by steady effusion and eruption rates, and hence a linear increase in cumulative volume. The former is typical of fissure eruptions and can be explained by tapping of an enclosed, pressurised system. The latter are typical of persistent Etnean summit eruptions, plus one persistent effusive eruption at Stromboli (1985–1986) examined here, and can be explained by overflow of the time-averaged magma supply. We use our effusion rate data to assess the magma balance at Etna (1980–1995) and Krafla (1975–1984). Between 1980 and 1995, Etna was supplied at a time-averaged rate of 6.8±2.3 m 3 s −1 of which 13% was erupted. At Krafla 817±30×10 6 m 3 was erupted and intruded during 1975–1984, and the ratio of erupted to intruded volume was 0.3. At Etna there is evidence for intrusion of the unerupted magma within and beneath the edifice, as well as storage in the central magma column. At Krafla unerupted magma was intruded into a rift zone, but an increasing proportion of the supply was erupted from 1980 onwards, a result of the rift zone capacity being reached. Magma intruded prior to an eruptive event may also be entrained and/or pushed out during eruption to contribute to the initial high effusion rate phases of Type I events. The detail in our effusion rate curves was only possible using a thermal approach which estimates effusion rates using satellite data. We look forward to analysing satellite-derived effusion rate trends in real-time using data from current and soon-to-be-launched sensors.

Improved identification of volcanic features using Landsat 7 ETM

Volcanic eruptions can present unpredictable hazards to populations living within regions containing potentially active volcanoes and for people traveling in jet aircraft that intersect with ash-laden eruption clouds. Methods of monitoring volcanic activity include searching for variations in the thermal signal from active fumaroles, lava domes, lava lakes, flows, and other features. Over many active volcanoes in the Western Hemisphere, low spatial resolution (4 km/pixel) weather satellite data acquired every 15 min are used to identify changes in eruptive activity, but are of insufficient spatial resolution to map active volcanic features. The Enhanced Thematic Mapper Plus (ETM+) on Landsat 7 can be used to monitor active volcanoes at a higher spatial resolution (15- to 60-m pixels). ETM+ also offers improvements over its predecessor, the Thematic Mapper of Landsats 4 and 5, by way of a 15-m panchromatic band and higher spatial resolution (60 m/pixel) thermal infrared (IR) band. With higher spatial resolution panchromatic data, we are able to map lava flow fields, trace very high temperature lava channels, and, at Lascar volcano, identify an arcuate feature associated with a collapsed crater floor, a phenomenon that may precede explosive activity. With improved spatial resolution in the thermal IR, we are able to map the bifurcation and braiding of underground lava tubes at Kilauea. Identifying tube locations and tracking their extension are important because, for a given volumetric lava production (effusion) rate, tube-fed flows can extend a much greater distance than surface flows. At both Kilauea and Etna, we are able to use the thermal data to estimate effusion rates, an important parameter for assessing how far a flow is likely to extend and therefore the hazard it poses. An improved ETM+ data collection and distribution system includes a well-formulated and -executed Long-Term Acquisition Plan and less expensive data that is available much faster than previously possible.

Radiative temperature measurements at Kupaianaha lava lake, Kilauea Volcano, Hawaii

Field spectroradiometer data in the wavelength range of 0.4–2.5 μm and spectral resolution of 1–5 nm have been used to compute the radiative temperature of the surface of Kupaianaha lava lake, Kilauea Volcano, Hawaii. Two sets of observations (a total of 120 spectra) were made on October 12, 1987, and January 23, 1988, when the lava lake was in a period of active overturning. The area of the surface for which temperatures were measured was ∼0.23–0.55 m2. Two numerical models of two and three components have been used to match the measured radiant flux ratios and to describe the surface of the lava pond in terms of radiant area and temperature. Three stages of activity on the lake surface are identified: Stage 1, characterized by magma fountaining and overturning events exhibited the hottest crustal temperatures (180–572°C) and the largest fractional hot areas (> 10−3). Stage 1 average flux densities were ∼2.2 × 104 W/m2, the highest recorded for the three stages of activity on either day. The largest radiative area of fresh magma was 29% at 1100°C, while cooling from magmatic temperatures to newly formed crust at 790°C took place in a matter of seconds. Stage 2, marked by rifting events between plates of crust, exhibited crustal temperatures between 100 and 340°C with fractional hot areas at least an order of magnitude lower than those found for stage 1. Average flux densities calculated for three examples of stage 2 activity were 5.3 × 103 W/m2. Stage 3, which was quiescent periods when the lake was covered by a thick crust, dominated the activity of the lake both temporally and spatially over 90% of the time. The characteristic crustal temperature of stage 3 was 80–345°C with most solutions near 200–300°C and fractional hot areas of ≤ 10−5 of the viewing area. Average flux densities for stage 3 were 4.9 × 103 W/m2. For many stage 3 examples, a two-component model was sufficient to describe the spectral data; however, for almost all of the stage 1 and 2 examples and the remainder of the stage 3 examples a three-component model was required. These determinations of lava temperature and radiant area have relevance for satellite and airborne measurements of the thermal characteristics of active volcanoes and indicate that temporal variability of the thermal output of lava lakes occurs on the time scale of seconds to minutes.

On the retrieval of lava-flow surface temperatures from infrared satellite data

The dual-band method has been widely used as the basis for determining lava surface temperatures from infrared satellite data; the method is based on the assumption that such surfaces can be described in terms of two end-member thermal components—hot cracks within a thermally homogeneous crust. The recent launch of the first orbiting hyperspectral imaging system, Hyperion, on- board the National Aeronautics and Space Administration Earth Observing-1 (EO-1) satellite heralds a new era of space-based hy- perspectral data collection that will allow more detailed models of lava-flow surface temperatures to be developed and parameterized. To this end, we have analyzed thermal images of active pahoehoe lava flows collected on Kilauea volcano, Hawaii, by using a forward- looking infrared (FLIR) 595 PM ThermaCAM, in order to assess the number of thermal components required to characterize the surface temperatures of active lava-flow surfaces. The FLIR images show that an active lava-flow surface comprises a contin- uum of temperatures that define distinctive temperature distribu- tions. Numerical model results reveal that the two-component dual- band method fails to resolve any of the major properties of the temperature distributions contained in these data (i.e., mode, skew, range, or dispersion). However, modeling five to seven thermal components allows all significant properties of the subpixel tem- perature distributions contained within the FLIR images to be de- termined. Thus, although the hyperspectral data provided by the EO-1 Hyperion yield as many as 66 wavebands in the 0.5-2.5 mm atmospheric window, useable data in 9-13 of these should be suf- ficient to perform accurate temperature characterization of active lava-flow surfaces from space.

Space-based estimate of the volcanic heat flux into the atmosphere during 2001 and 2002

Satellite remote sensing offers a convenient way to monitor changes in the thermal budgets of Earth’s subaerially active volcanoes. By using data acquired by the National Aeronautics and Space Administration’s Moderate Resolution Imaging Spectro-radiometer, we have calculated the amount of heat released into the atmosphere by 45 volcanoes active during 2001 and 2002, in order to quantify the contribution active volcanism makes to Earth’s energy budget. We report that the amount of heat radiated into the troposphere by these volcanoes, as detected from space, was ;5.34 3 10 16 and 5.30 3 10 16 J/yr during 2001 and 2002, respectively. This energy flux is three orders of magnitude less than the amount of energy consumed by the United States of America for residential, manufacturing, and transportation purposes during 1999.

The thermal stealth flows of Santiaguito dome, Guatemala: Implications for the cooling and emplacement of dacitic block-lava flows

Thick, slow-moving block-lava flows are associated with extrusive activity in dacitic systems, where lava-core depressurization during flow-front collapse generates devas- tating block-and-ash flows. Dimensional and rare thermal data collected during Jan- uary 2000 for an active dacitic block flow at Santiaguito (Guatemala) provide insight into cooling and emplacement mechanisms. Flow velocity was low (12.5 m·d 21 ), in spite ginal shear zones. The axial part of the flow front was thicker than the marginal zones and was oversteepened. This geometry can be explained by a higher vertical velocity gradient in the axial zone, causing more frequent and larger-volume flow-front col- lapses. Axial-zone collapses also penetrate farther up flow, but not sufficiently to de- pressurize the flow core and generate a block-and-ash flow. For such a block-and- ash flow to occur, we calculate that an in- crease in velocity and/or thickness (due to increased slope or topographic confine- ment) must occur. Whereas low surface temperatures make block flows invisible to short-wave infrared sensors, the low veloc- ity also contributes to the stealthy behavior of these flows. Their stealthy nature, how- ever, masks the fact that they can extend many kilometers, moving block-and-ash flow sources closer to vulnerable communities.

Remote monitoring of Mount Erebus Volcano, antarctica, using Polar Orbiters : Progress and Prospects

Mount Erebus (Antarctica) is a remote and inhospitable volcano, where field campaigns are possible only during the austral summer. In addition to continuously monitoring seismic instruments and vid...