Frequently Asked Questions

The MODerate-resolution Imaging Spectroradiometer (MODIS) is an instrument that is aboard two satellite platforms owned by NASA: Terra (launched December 18th, 1999) and Aqua (launched May 4th, 2002). The MODIS instrument has 36 spectral bands available to view the Earth. Each instrument has a viewing swath width of 2,330 km and views the entire surface of the Earth every one to two days. The image resolution used in detecting fires is 1 km. For more information on this instrument, please see the MODIS website: http://modis.gsfc.nasa.gov/

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Q: How does MODIS detect fires?

A hotspot/fire is detected by MODIS using data from the middle infrared and thermal infrared bands. These detections are produced using the same algorithm as the standard MODIS MOD14 fire and thermal anomalies product. The algorithm examines each pixel of the MODIS swath, and ultimately assigns to each one of the following classes: missing data, cloud, water, non-fire, fire, or unknown. In most cases, this thermal anomaly is a fire, but sometimes it is a volcanic eruption or the flare from a gas well. We have no way of knowing which it is based on the MODIS data alone.

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Q: When were the Terra and Aqua satellites launched?

Terra was launched 18 December 1999 and Aqua was launched 4 May 2002. Fire Data are available from November 2000 onwards.

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Q: How often are the data provided?

The Terra MODIS instrument acquires data twice daily (10:30 am and 10:30 pm), as does the Aqua MODIS (2:30 pm and 2:30 am). Therefore, four daily MODIS observations are available to contribute to global fire monitoring.

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Q: Does topography affect fire detections?

Topography affects fire detection much less than for reflected light, such as in an optical landsat or radar.

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Q: How does the effect of shadows from either clouds or view angle affect fire detections?

Cloud shadows do not have an effect. The fire detection algorithm measures fire emissions versus background ground temperature - it does not measure sunlight. However, view angle is important. The wider the view, the larger the pixel field of view (the ground space covered). As a result, you would need a proportionately larger fire area for the same likelihood of detection for most algorithms. This necessity is incorporated into quality control reporting.

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Q: How does air temperature affect fire detection?

Fire detection algorithms rely on ground temperatures for comparison with fire emissions. However, warmer areas like sandbeds, rock outcrops, etc., can come out as false positives. Filters incorporated into the algorithms attempt to correct for this.

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Q: Why do you not see the same fire twice if the satellite passes over the location 4 times?

This is due to the dynamic and diurnal patterns associated with fire. Fires move across the landscape at varying rates, depending on multiple factors including, for example, the underlying vegetation type and the specific characteristics of the fire, and therefore may be present in different locations when the sensors pass overhead. In addition, the inherent diurnal burn-up and die-down patterns of a fire can impact whether one can see the same fire twice.

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Q: What is UTC?

Coordinated Universal Time (UTC) is a high-precision atomic time standard. UTC replaced Greenwich Mean Time (GMT) as the World standard for time in 1986. It is based on atomic measurements rather than the earth's rotation.

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Q: What is the conversion from UTC to Madagascar time?

To obtain Madagascar time, add 3 hours to UTC.

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Q: What time does the satellite pass over Madagascar?

The satellite pass is different each day. To estimate when there will be a pass over your area of interest, please see the following tool: http://earthobservatory.nasa.gov/MissionControl/overpass.html

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Q: What size fires can be detected?

Under ideal conditions the smallest flaming fire that can be routinely detected (i.e. near 100% probability of detection) is approximately 50 square meters in size. These are conditions such as when a fire is observed at (or near) nadir on a fairly homogeneous surface, no other significant fires are nearby, and the scene is free of clouds, heavy smoke and sun glint. In any given scene the minimum detectable fire size is a function of many different variables (scan angle, biome, sun position, land surface temperature, cloud cover, amount of smoke, wind direction, etc.), so the precise value will vary slightly with these conditions.

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Q: What are the limitations of this resolution?

An active fire is displayed as a 1km pixel on the ground; the fire "location" is the center point of that pixel. This does not necessarily mean that the fire is 1km in size. While we are not able to determine the exact fire size, what we do know is that at least one fire is located within that 1km pixel. If multiple fires are detected within the same 1km square location, the system will only display one pixel for that area. Sometimes you will see several active fires in a line. This generally represents a fire front.

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Q: Who can receive the data?

Anyone that has an e-mail account can receive the alerts.

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Q: How much does it cost to receive the alerts on a daily basis?

At the moment there is no charge for this service.

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Q: What is the delay from the time the satellite passes until an alert is emailed?

The delay is approximately 1 day. Data is compiled for an entire 24-hour period and then processed through an automated system. The automated system will run each day, including weekend and holidays.

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Q: Who owns the data? How do we cite these in publications?

Please contact the Fire Alerts Team using the Contact Us link at the bottom of the page to discuss any specific distribution of the data by your organization. Permission is granted on a case-by-case basis and at this time there is no charge associated with permission or the alert service. All other data restriction questions can be sent to this address as well.

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Q: What do I do when my email address changes?

To update your contact information or manage any aspect of your subscription, please access our website. Enter your login information and you will see options to edit your contact information, subscriptions, or unsubscribe. Please note that your email address is your login information, and if updated your login information will also change.

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Q: Can I request data for someone else?

We would prefer all users directly subscribe to the alerts system. However, if there are specific limitations that prevent this, individuals can forward the data to another user with the strict instructions of not altering any data, disclaimers, or partner information. Please contact the Fire Alerts Team using the Contact Us link at the bottom of the page to notify us if this is your intention.

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Q: I did subscribe, but I am not receiving emails.

Sometimes, your e-mail client flags some messages as SPAM, and these messages are automatically filtered out of your inbox. Add us to your secure e-mail list to avoid that problem.

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Q: Who provides the data used in the alerts system?

The data is provided through a collaborative project involving NASA's MODIS Rapid Response System, the Fire Information for Resource Management System (FIRMS), University of Maryland, and the Center for Applied Biodiversity Science at Conservation International.

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Q: What does each of the columns in the alert mean?

AreaName - area of interest (for example, district name, protected area name, etc.)

Latitude - the north or south location on the earth measured in decimal degrees

Longitude - the east or west location of the point on the earth measured in decimal degrees

Date - date the fire was detected

Time - time the satellite passed over the location, provided in UTC

Satellite - platform that observed fire, there are two MODIS instruments - Aqua and Terra. For more information on these platforms, see the information on MODIS in the first question

Confidence - The confidence value is based on a collection of intermediate algorithm quantities used in the detection process. The range of confidence is expressed between 0-100 (the values range from 0=very low to 100=very high). The confidence field is experimental and should be used with caution; it is likely that it will vary in meaning in different parts of the world

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Q: How do I view the text file attachment in the alert emails using Microsoft Excel?

Text file attachments are provided as comma-delimited files. They may be directly imported into Microsoft Excel and separated into columns using the "text to column" wizard under the Data menu.

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Q: What are the data restrictions?

Please contact the Fire Alerts Team using the Contact Us link at the bottom of the page to discuss any organized studies for publications that intend to use the data. Permission is granted on a case-by-case basis and at this time there is no charge associated with permission or the alert service.

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Q: How can I get historical data on fires?

Organizations within Madagascar may contact Solofo Ralaimihoatra (the CI-Madagascar Fire Outreach Coordinator) at 'sralaimihoatra at yahoo.fr'.

Organizations outside of Madagascar may contact the Fire Alerts Team using the Contact Us link at the bottom of the page.

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Q: How can I get more information on each of the organizations involved?

Please see our partners page.

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Q: How can I get burned area information?

Unfortunately at this time we are unable to provide burned area information or links to alternate data products. We continue to research potential opportunities and will post updates as available.

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Q: How can I get the information on where the clouds are for that day?

Cloud cover can prevent some fires from being detected. An indication of cloud cover is not yet included in the alerts system. If you want to know whether the MODIS Rapid Response System may have failed to detect some fires due to cloud, you can look on the MODIS Rapid Response Real-Time website. There you can view the MODIS near-real-time level 2 browse images which clearly show cloud cover at the time of overpass.

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Q: Where else is the data available?

There is a new Global Fire Alerts program led by University of Maryland: http://maps.geog.umd.edu/alerts/

The program first allows you to specify your own geographic area of interest (AOI). Then, any time MODIS active fires are detected in or around your AOI, you will be sent an email alert that notifies you of the fire locations. You can specify your AOI in any of three ways:

By defining its bottom left and top right coordinates

By selecting a protected area, with buffer options of 5, 10, or 15 kilometers

An interactive map

You can customize your email alert by choosing to receive:

Text that gives the locations of detected fire, along with an image that shows the fires

Just the fire locations text, with a link to the image

Further, you can also choose to receive a Comma-Separated Text File (CSV) containing all the detected fire points. You can import this file into your desktop GIS for further analyses. All email alerts include the geographic coordinates of pixels flagged as containing at least one fire, the time and date of data satellite acquisition and a confidence value.

This is a beta version, which means that improvements are still planned for this service. It is also automated so that if there are fires in your area of interest, you will receive an email every day - including all weekends and holidays - at a consistent time each day.

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Q: Where can I get additional FAQ resources on MODIS fire detection products?

University of Maryland Fire Information for Resource Management System (FIRMS) FAQs: http://maps.geog.umd.edu/firms/faq.asp

MODIS Rapid Responses System: http://rapidfire.sci.gsfc.nasa.gov/faq/

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