Satellite Downlink

PRINCIPLE CONTACT

Bryce Nordgren, Physical Scientist

INTRODUCTION

The MODIS direct broadcast receiving station allows us to receive timely information about fire starts and fire progress.

We receive data collected from the MODerate resolution Imaging Spectrometer (MODIS) instrument on-board the Terra and  Aqua satellites. The satellites orbit such that every location on the Earth is observed four times daily, twice during the daytime and twice at night. As the raw data are downlinked, they are processed to detect which pixels contain fire and which pixels appear to be burned. We then use this information as inputs to our air quality forecasting model.

FUNCTION AND OBJECTIVES

In short, MODIS satellite images let us see the big picture. Between the two instruments (one on Terra and one on Aqua), the entire earth is imaged four times a day. As shown on the left, MODIS captures which segments of the fire are most actively burning (red outlines) and records the smoke situation over a wide area. MODIS has a spatial resolution of 1 square kilometer on the thermal channels, meaning that even though we can know the center location of the pixel to less than 100 meters, we cannot tell precisely what part of the pixel's square kilometer signalled a fire detection. So the satellite data gives a good overall view of fire activity, but not enough detail to be useful to the people on the ground fighting the fire.
MODIS does not actually detect fire. It takes pictures of the earth in many different colors of light, most of which are invisible to the naked eye. Specialized algorithms, designed to work with the particular bands collected by MODIS, analyze these pictures for specific purposes. One purpose is to detect "Fire and Thermal Anomalies" (which, by the way, also detects the US Steel plant on Lake Michigan.) Another purpose is to detect areas of the ground which "look burned". Still other purposes are to gauge the health of vegetation and estimate various fire danger indices. If we think up something else that these data can be used to tell us, we can apply the new algorithm retroactively to old data. By retaining the raw data, we are able to detect trends in fire activity over time by processing the data consistently instead of just using data which was processed with the "current algorithm" as it improved over the years.

METHODS

The main advantage to owning a receiving station is that it makes our air quality modeling system possible. The information we glean from the satellite observations is collected over the entire nation (as shown to the right) and then used to initialize the smoke dispersion forecast. The key point is that satellite observes the nation in swaths which are approximately 1000 miles wide. Once all the daytime data are in, we can calculate actual fire growth since the last observation, update our predictions of fire activity, and run a smoke dispersion forecast. Likewise, a forecast may be run once all the nighttime data are in. Our receiving station provides near real time reporting on fire activity which is both comprehensive and uniform.
Occasionally, our MODIS receiving station is pressed into service of firefighters, but perhaps not in the way one might expect. As mentioned above, MODIS cannot locate the precise position of a fire within a one square kilometer pixel. Note also that MODIS only observes the fire four times a day. If a fire is already staffed, the people on the ground are going to know the position of the fire more precisely than MODIS will, and they are going to be continually monitoring the fire's progress very carefully. The people who can most benefit from MODIS data are those who are interested in the big picture, because that is what MODIS provides. We integrated with a Multi-Agency Command (MAC) group in 2003 when it formed to coordinate firefighting efforts over all of central and western Montana, as well as Idaho. The MAC was able to use MODIS data as another tool to help them decide how to disseminate resources and identify new fire starts adjacent to crews already deployed.

FUNDING ORGANIZATION

National Fire Plan