Thread by @MappingSupport

1/14 I have been volunteering to produce online wildland fire maps for about the last 10 years. This is a multi-part tweet to help people understand satellite hotspot data for wildland fires.

2/14 The #1 thing to know is that any fire data you see on maps is **not real time**. After a satellite pass it takes NASA ~3 hours to process the raw data before it can be displayed on any map.

3/14 Since data you see via an online map is **not real time**, never rely on any map (or anything else) to ignore an order to evacuate. The professionals that make decisions which areas must evacuate have more information than is available to you.

4/14 There are 2 MODIS satellites and 2 VIIRS satellites. Altogether, these satellites make a total of 8 passes each 24 hours. For the West Coast, very rough timing is midnight to 3am (4 passes) and noon to 3pm (4 passes).

5/14 Data from the 4 nighttime passes will show up on maps in the morning - spread over a few hours. Data from the 4 daytime passes will usually show up on maps in the late afternoon to evening.

6/14 Each ‘hotspot’ is actually an area. The heat source can be anywhere inside that area.
MODIS area = 1km (about 3,280 x 3,280 feet)
VIIRS area = 375m (about 1,230 x 1,230 feet)

7/14 Each satellite pass senses a strip of ground. Sometimes there will be ‘false positive’ heat detections near the edge of the strip. This can happen when a fire is making a huge smoke plume that is carrying hot debris.

8/14 A grass area can burn and then cool in between satellite passes. When that happens the area might never appear on the maps as a hotspot. Also, a smoldering fire might not be hot enough to be detected.

9/14 NASA FAQ:
earthdata.nasa.gov/faq/firms-faq

Satellite hotspot data can be downloaded from:
firms.modaps.eosdis.nasa.gov/active_fire/#f…

10/14 The wildland fire maps that I post will show new satellite data (if there is any available) at the top of the hour. You have to re-open the map to see any new data.

11/14 Satellite legend for my maps.
MODIS = Red triangle
VIIRS = Orange squares
If the map is zoomed out then VIIRS data might run together into a big orange blob.

12/14 The maps I post have a variety of #GIS overlay layers that you can turn on/off/restack. Many of the layers are clickable to display more data. For help with the map please click “Map tips” upper left corner.

13/14 To make your own custom map link, click
Menu ==> Link to this map. The link that is displayed will replicate the map on your screen.

14/14 To see my other projects you can check out mappingsupport.com

@threadreaderapp unroll