Unit 3 Infrared Basics and Limitations

Objectives: The student will be able to explain in layman’s terms four basic elements that affect thermal IR sensing and interpretation The student will be able to identify the limitations of all infrared systems.

Unit Contents 1. Objectives 2. IR Basic Physics 3. IR Limitations

Infrared Basics The four basic elements to consider in thermal IR sensing and interpretation are: The source (the fire) Attenuation Sensor or detector The remote sensing analyst and/or image interpreter

Source (the fire) The energy from fires, heat, is emitted as electromagnetic (EM) energy within specific wavelength bands. Energy from fires is emitted at long wavelengths. Most fire mapping applications utilize long- wavelength thermal remote sensors.

We are dealing with Thermal Infrared Not all IR is heat Reflective Thermal

Attenuation The scattering or absorption of electromagnetic energy by the atmosphere. The atmosphere is a good transmitter of IR energy in two regions (called windows) 3-5 µm and 8-14 µm

Sensor or detector Ideal sensor design considers The sources it is designed to measure The atmospheric windows for those wavelengths The most suitable materials to build the detector

Thermal Bands Visible Near- and Mid-IR Thermal IR

Concurrent Burn Imagery Thermal imagery from an low level UAS Multi-spectral EO/IR imagery from the NASA AMS Wildfire sensor

USDA Forest Service MODIS Active Fire Mapping Program October 26, :35 UTC Terra MODIS True & False Color Composite

Remote Sensing Analyst or Image Interpreter Training Experience Time Situation Customers expectations

Infrared Limitations Attenuation Solar Radiation Heat Source Temperature Saturation ALL infrared sensors are limited by the physics of thermal infrared energy

Attenuation Thermal IR energy can be emitted or reflected. During fire/heat-mapping missions we are usually looking for emitted energy (fires) Water and water vapor absorb IR energy (e.g., clouds or fog) The atmosphere is a good transmitter of IR energy in certain regions (remember the two windows)

Image Credit: FLIR Infrared will not pass through water.

Marine Layer (Fog) Mendocino June 29, 2008

High Clouds – Battle Creek Complex July 27, 2007, Eastern OR

White-hot vs. Black-hot Phoenix Imagery is black-hot.

Solar Radiation Reflected sunlight may mix with emitted IR energy. Highly reflective surface may appear hot in IR imagery. Creates false positives. Long-wavelength (8-14 µm) data is collected to portray background areas. IR missions scheduled to maximize the thermal difference between fires and background.

Energy Detection

Heat Source Temperature The amount of energy emitted by a fire or heat source depends on the temperature of the object. Fires are not perfect emitters of IR energy Emitted energy can be absorbed by heavy canopy or overstory Thermal remote sensing can only detect heat on the surface of targets.

Fire Engine Road Heat from burning grass Photo Point B 1:00 PM

Fire Engine Road Burn Area Photo Point B

Fire Engine Road Heat from burning grass Photo Point B 1:00 PM

Other hot objects

Saturation Very hot object or heat sources may saturate a sensor, creating low contrast in the image. Blooming is caused by hot gasses when a fire flares up. Gasses in the convective fire column can be hot enough to saturate the sensor and render portions of the imagery unusable.

Roundabout - 5/01/07, Southeastern GA

Heat from the engines is saturating the sensor Crewmember can be seen through the open hatch Pilot cannot be seen through windshield

Objectives: The student will be able to explain in layman’s terms four basic elements that affect thermal IR sensing and interpretation The student will be able to identify the limitations of all infrared systems.

Questions?