Optoelectronics Radiometry and Photometry, Emitters and Receivers

Radiometry and Photometry Radiometry is measuring radiation brightness within a fixed band of wavelengths. Photometry is measuring visible and ultraviolet light radiation brightness.

Uses  Uses for this type of sensing apparatus would be: Satellite technology Astronomy Digital photography These instruments are a lot like eyes. They rely on waves of scattered and emitted electromagnetic radiation as their means for gathering information.

Electromagnetic Radiation All objects that are not at absolute zero temperature emit electromagnetic radiation in the form of waves of energy. Electromagnetic radiation occurs over a continuum of wavelengths from very long radio waves to extremely short gamma rays. The ordered arrangement of electromagnetic radiation as a function of wavelength is called the electromagnetic spectrum.

Reflection, Absorption, Transmission When electromagnetic energy strikes a material, three types of interaction can follow: reflection, absorption and/or transmission.

Reflection Our main concern is with the reflected portion. It is usually this which is returned to the sensor system. Exactly how much is reflected will vary, and will depend upon the nature of the material and where in the electromagnetic spectrum our measurement is being taken. As a result, if we look at the nature of this reflected component over a range of wavelengths, we can characterize the material.

Passive/Active Sensors Radiometry and photometry sensors can be divided into two broad groups -- passive and active. Passive sensors measure ambient levels of existing sources of energy. The earliest example of this is photography. Active sensors provide their own source of energy. Radar systems emit energy in the microwave region of the electromagnetic spectrum. The reflection of that energy by the earth’s surface material is then measured to produce an image of the area sensed.

For any sensor to work it needs to be able to send and/or receive information. They are able to do this with emitters and receivers:  Emitter broadcasts a signal  Receiver receives the signal Emitters and Receivers

For example the National Weather service uses Doppler Radar. 1. The radar tower emits a signal from its emitter. 2. The signal travels through the atmosphere until it strikes an object, clouds, water vapor, etc. 3. The signal is bounced back to the radar tower’s receiver which receives the signal and in turn makes it functional for acceptable usage.

An additional example is sonar. The same sequence of events occurs with sonar. In a submarine an emitter emits a signal which is bounced off an object and received by the transducer. The transducer is a type of receiver that converts sonar waves into a usable signal. Emitters and Receivers