thermal anomaly

^{ALASKA VOLCANO OBSERVATORY GLOSSARY}

A thermal anomaly can be defined as an unexpected increase in the radiant temperature of a pixel relative to its neighbors. Its neighbors may be considered as pixels next to it in the same image and same band, or pixels in a different band, or even pixels as they change through time. In other words, the anomaly can occur within the spatial, spectral and temporal domains. The term thermal anomaly does not carry with it any indication of the cause of the anomaly. In this case, the goal is to find thermal anomalies that are the result of volcanic activity. The causes of thermal anomalies include:

1) Volcanic activity, e.g., warming of the ground, lavas, pyroclastics, gas and ash emissions.

2) Solar reflections from peaks or meteoric clouds near the volcano, solar heating of rocks.

3) Thermal contrast increases at lakes when the background drops below lake temperature.

4) Clouds or vapors from fumaroles may obscure anomalies, or reflect sunlight.

5) Changes in the atmospheric conditions may favor or hinder (dry vs. wet) detection of warm areas.

6) Geometric constraints from the satellite's orbit and ground topography, an anomaly may be hidden from view by a crater wall.

7) Noise in the sensor or in the reception of data.

8) Natural or anthropogenic signals such as fires.