<title>Multiscale thermal-infrared measurements of the Mauna Loa caldera, Hawaii</title>

Abstract

Until recently, most thermal infrared measurements of natural scenes have been made at disparate scales, typically 10 -3 -10 -2 m (spectra) and 10 2 -10 3 m (satellite images), with occasional airborne images (10 1 m) filling the gap. Temperature and emissivity fields are spatially heterogeneous over a similar range of scales, depending on scene composition. A common problem for the land surface, therefore, has been relating field spectral and temperature measurements to satellite data, yet in many cases this is necessary if satellite data are to be interpreted to yield meaningful information about the land surface. Recently, three new satellites with thermal imaging capability at the 10 1 -10 2 m scale have been launched: MTI, TERRA, and Landsat 7. MTI acquires multispectral images in the mid-infrared (3-5µm) and longwave infrared (8-10µm) with 20m resolution. ASTER and MODIS aboard TERRA acquire multispectral longwave images at 90m and 500-1000m, respectively, and MODIS also acquires multispectral mid-infrared images. Landsat 7 acquires broadband longwave images at 60m. As part of an experiment to validate the temperature and thermal emissivity values calculated from MTI and ASTER images, we have targeted the summit region of Mauna Loa for field characterization and near-simultaneous satellite imaging, both on daytime and nighttime overpasses, and compare the results to previously acquired 10 -1 m airborne images, ground-level multispectral FLIR images, and the field spectra. Mauna Loa was chosen in large part because the 4x6km summit caldera, flooded with fresh basalt in 1984, appears to be spectrally homogeneous at scales between 10 -1 and 10 2 m, facilitating the comparison of sensed temperature. The validation results suggest that, with careful atmospheric compensation, it is possible to match ground measurements with measurements from space, and to use the Mauna Loa validation site for cross-comparison of thermal infrared sensors and temperature/emissivity extraction algorithms.

Turbulence-induced spatial variation of surface temperature in high-resolution thermal IR satellite imagery

“…No spatial emissivity features have been identified in ground sample measurements or in a previous study by Balick et. al 4 . However, spatial variations of temperature can be caused by unknown subsurface variations.…”

“…The figure reveals a thermal "wave" that propagates in both the z and -z directions and illustrates the relevant features of Eq. (4) Technically, this equation does not hold for a subsequent event because the boundary conditions used to derive Eq. (3) no longer hold.…”

“…However, most satellite thermal imaging sensors have too coarse of a resolution to observe these variations as they average over large areas and, to our knowledge, no one has looked for them. During a field campaign conducted jointly by scientists of the US Department of Energy's Multispectral Thermal Imager 3 (MTI) and the U. S. science team for the Advanced Spectral Thermal Emission Spectrometer (ASTER) at the Mauna Loa (Hawaii) caldera, strong evidence of the effects of transient eddies on observed surface temperatures were observed 4 . During this campaign, moving spatial temperature patterns on the scale of 10s of meters were observed with an uncalibrated thermal video system from the caldera rim, radiometric point measurements of surface temperature fluctuated by about 3K over periods of 2 -3 minutes, and the MTI observed temperature patterns over an area of nearly uniform emissivity.…”