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A.F.R Quiz 2
| Question | Answer |
|---|---|
| An Alternate Light Source (ALS) | employs tunable wavelengths used in the discovery of different forms of evidence |
| ALS | emit radiation across the entire electromagnetic radiation spectrum from UV to infrared (IR) |
| The surface or physical properties of an item | will either reflect, transmit, or absorb light |
| Electromagnetic radiation (ER) | is energy moving in a wave like motion |
| ER includes | X-rays, UV radiation, visible light, IR radiation, thermal radiation, radio waves and microwaves |
| X-rays, UV radiation, visible light, IR radiation, thermal radiation, radio waves and microwaves Also referred to as the | “electromagnetic spectrum |
| When visible light is refracted through a prism it | displays a colour range of red, orange, yellow, green, blue, and violet |
| Red at 700 nm, | has a lower frequency and less energy |
| Blue at 400 nm, | has a higher frequency and more energy |
| There are three primary characteristics of light; | 1. Wavelength 2. Frequency 3. Speed |
| In a vacuum all ER travels | at the “speed of light” = 299,792,458 meters per second |
| Short wavelength (towards UV) = | high frequency |
| Long wavelength (towards IR) = | low frequency |
| Wavelengths are measured in nanometers (nm) | 1nm = 1 billionth of meter |
| Three areas of the electromagnetic radiation spectrum; | Near ultraviolet area = 300 - 400nm Visible area = 400 - 700nm Near infrared area = 700 - 1100nm |
| When contacting a surface, electromagnetic radiation can be, | 1. Reflected 2. Absorbed 3. Transmitted |
| Reflected | Specular - light strikes a smooth surface (A) and reflects at the same angle and parallel. Diffused - rough or textured surface (D). Light is scattered and not parallel |
| Absorbed - some or all the light is absorbed (B). | If all absorbed = black If all reflected = white Absorbed light converts to either heat or luminescence (molecules or atoms are in an excited higher energy state) |
| There are two types of luminescence | Fluorescence Phosphorescence |
| Stokes Shift | Fluorescence, was coined by Sir George Stokes in 1850. Fluorescing light has a longer wavelength than incident radiation |
| Phosphorescence | range of luminescence is several seconds after emitting radiation is discontinued |
| Fluorescence | emission lasts about one second after emitting radiation is discontinued |
| Luminescence Is used in a variety of forensic applications for locating evidence, such as; | 1. Gunshot residue (GSR) 2. Fibers 3. Biological fluids 4. Inks 5. Fingerprints |
| Incandescence | Light is emitted from an object that has been heated. “Glows” when it’s hot, like molten rock. Glass and some metals will glow when heated. Luminescence is caused by the addition of heat |
| UV and IR are either | absorbed or reflected by different types of surfaces. |
| UV will | not penetrate the surface of skin, but fine details on the surface are accentuated. |
| IR penetrates the skin, | 2-3mm, so objects like veins can be seen. |
| IR photography | helps to create contrast on multi coloured or dark surfaces |
| Sensors in today’s cameras are sensitive | from 350 to 1000nm |
| In the 19th and early 20th century identification of criminals relied on the | Bertillon System and Henry Classification |
| 1960s 70s | AFIS developed |
| 5 fingerprint reader systems, called | “the Finder |
| The Finder” was used for 3 years to convert | 15 million fingerprint cards. |
| Biometrics - | refers to using unique biological measurements or features to identify individuals. From the root word “bio” meaning life and “metric” meaning measure |
| Anthropometry was | the first method of criminal identification using biological measurements |
| Fingerprints replaced | anthropometry as a more reliable means of individualization |
| Fingerprint biometrics were the first to | digitize for analysis by a computer |
| Three Fundamental Stages of AFIS | 1. Data acquisition - senses fingerprint to be recognized. 2. Feature extraction - a pattern is extracted from the sensed image. 3. Decision making - information extracted from the recognized image is compared with images stored in the system. |
| Difference between AFIS and IAFIS. | AFIS is a stand-alone within an agency. IAFIS is Integrated, linking agencies together to compare and share evidence. |
| The two main purposes of AFIS for law enforcement are to, | 1. Determine if a person has a previous criminal record. 2. Conduct searches of crime scene prints |
| The data is obtained by: | 1. Inked Tenprint sheets scanned into the system. 2. Livescan - digitizes impressions and loaded directly into AFIS. Most law enforcement agencies now use Livescan rather than ink impressions. It is easier, faster, and cleaner. |
| Rolled impressions can have more than | 100 minutiae, whereas crime scene prints will have fewer |
| Coding Prints | Computer id minutiae, Algorithm detect minutiae, Recognizes ridge flow, distance between ridges Returns a list of probable's, based on the location of the minutiae with similar features. Examiner will then check if minutiae are the same & make the id |
| AFIS can correctly find a latent fingerprint with | only 6 points 86% of the time and 61% of the time with a palm |
| Examiner must | input special prints like amputations, temporary and permanent injuries. |
| Livescan is | inkless device which can capture digital images of finger and palm prints, then electronically transmits them to AFIS |
| Advantages of livescan | Electronically stores images. Eliminates large storage capacities for millions of ten print forms. Faster and cleaner process. No ink required and scanned directly into the system |
| advantages of livescan | Prints can be shared electronically with other agencies, Livescan systems have become more affordable, and smaller agencies can now acquire their own systems. Technology keeps improving in accuracy. Using Livescan is like ink and paper. |
| polychromatic | have two or more monochromatic bands. Blue with yellow bands produce green |
| monochromatic | Monochromatic band, has a narrow range of colours. The narrower the band, the more monochromatic the light will be |
| The band of light is determined by its central wavelength (CW) and its bandwidth (BW). | Central Wavelength = midpoint of the bandwidth |
| Barrier Filter | Intended to suppress or block (absorb) certain wavelengths and permit only selected wavelengths to pass through. These help to eliminate backgrounds. Blocks reflected light and transmits the fluoresced light |
| Bypass Filter | Allows a limited range of wavelengths to be recorded and blocks all other colour. Used with ultraviolet (UV) which only allows the ultraviolet range of wavelength |
| specular | light strikes a smooth surface (A) and reflects at the same angle and parallel |
| Diffused | rough or textured surface (D). Light is scattered and not parallel |
| lu·mi·nes·cence | the emission of light by a substance that has not been heated, as in fluorescence and phosphorescence |
| Stokes shift | Fluorescence, was coined by Sir George Stokes in 1850. Fluorescing light has a longer wavelength than incident radiation |
Created by:
skyep25