Narrow band sensor

If we have narrow-band sensors where each sensor responds to a single wavelength X, with i e r, g, b, then the intensity /, measured by the sensor is simply the product of a geometry factor G, the illuminant L,(x, y) at the corresponding object location (x, y) and the reflectance R at this location. 

The IR detector utilizes a combination of three IR sensors of extremely narrow band response. One covers the typical CO2 emission spectral band, and the two other sensors cover different adjacent specially selected spectral bands. While the CO2 emission band sensor is responsible for the detection of... 

Luminescence Lidar (light Detection and Ranging) is an active instrument, which sends out coherent waves to the object concerned. A fraction of the transmitted energy is transformed by the objects and sends back to the sensor. lidar instriunents measure both the traveUng time interval between sensor/object/sensor as well as the difference between emitted and returning energy, providing information on the exact position of the objects and on the material the objects are made of. Spectral selectivity was achieved usually with the aid of narrow band interference filters. 

Suppose that we have two different illuminants. Each illuminant defines a local coordinate system inside the three- dimensional space of receptors as shown in Figure 3.23. A diagonal transform, i.e. a simple scaling of each color channel, is not sufficient to align the coordinate systems defined by the two illuminants. A simple scaling of the color channels can only be used if the response functions of the sensor are sufficiently narrow band, i.e. they can be approximated by a delta function. 

In Chapter 3 we have seen that sensors that have very narrow band-response functions simplify the functions which relate the energy measured by the sensor to the geometry of the object, the reflectance of the object patch, and the irradiance falling onto the patch. If the response function is very narrow, it can be approximated by a delta function. In this case, the energy measured by a sensor I at sensor position X/ is given by... 

For all of the following algorithms, we will assume that the response functions of the sensors are very narrow-band, i.e. they can be approximated by delta functions. Let A., with i r,g, h) be the wavelengths to which the sensors respond. We will now denote the sensor coordinates by (x, y). The intensity measured by the sensor at position (x, y) is then given by... 

Assuming narrow-band camera sensors that only respond to wavelength X, with i e r, g, b, we obtain... 

Finlayson and Hordley (2001 a,b) have developed a method for color constancy at a pixel. They make two assumptions. One that the camera s sensors are sufficiently narrow band and that the illuminant can be approximated by a black-body radiator. If the sensor s response functions are not sufficiently narrow band, a sharpening technique can be used (Barnard et al. 2001 Finlayson and Funt 1996 Finlayson et al. 1994a,b). The power spectrum of a black-body radiator was described in Section 3.5. The radiance of a black-body radiator at a temperature T, measured in Kelvin, at wavelength /. is given by (Haken and Wolf 1990 ... 

Funt and Finlayson (1995) proposed histogramming of color ratios. They suggested computing the ratios between adjacent pixels. Let c = [cr, cg, ct]T and c = [c, c g, c h 1 be two colors that are obtained from two adjacent pixel positions. Assuming that the sensors are narrow band, the intensity measured by the sensor at position (x, y) is given by... 

Dividing by one of the channels has the advantage that geometry information, which is constant for all three channels, is automatically removed. A nonwhite illuminant scales the three color channel by S(.s>, sg, Sb) as discussed in Section 4.6, provided that the camera s sensors are sufficiently narrow band. Therefore, two chromaticity distributions % and % of the same object in ( i, 2 ) chromaticity space are invariant up to a translation, i.e. 

The visible and infrared sensors are fast, but are subject to many false signals from artificial light, sunlight, hot bodies and other heat producing bodies. The ultraviolet (UV) sensor is fast in response and is affected by few extraneous signals which are controllable. The UV sensor must be the type that only responds to a narrow band of UV, from 1850 Angstroms to 2450 Angstroms. 

Both broad-band light sensors, measuring total quanta 400-700 nm, and narrow-band light sensors, at 460 10 nm and 550 10 nm, are used. From the measurement at 460 nm, the total quanta 350-700 nm can be calculated (i5). From the measurements at 460 and 550 nm, the attenua-... 

Only for particular molecules, e.g. ammonia because of its strong lines in the 20-40 GHz region, or water at 22 GHz because there is no other line until 183 GHz, would spectral considerations force the worker to lower frequencies. The 20-40 GHz band is also attractive, however, because of the cheap sources and low-noise semiconductor detectors, manufactured for movement sensors and short-path wireless links. The projected automobile collision-avoidance radar systems will make cheaper sources and detectors available for the 60-70 GHz region within the next few years. The 60 GHz across-office circuits for wireless data links could provide useful narrow-band sources for oxygen determination. The 35 GHz and 94 GHz close-range radar bands provide a useful reservoir of components and sources for the potential manufacturer of MMW spectrometers. 

The radiation - normally visible and/or Near and Short Wave IR, and/or thermal emissive in nature - must then be broken into its spectral elements, into broad to narrow bands. The width in wavelength units of a band or channel is defined by the instrument s spectral resolution. A more vital aspect of sensor characteristic and performance is spatial resolution. Spatial resolution represents the ability to recognize and separate features of specific sizes. The common definition of spatial resolution is often simply stated as the smallest size of an object that can be picked out from its surrounding objects or features. This separation from neighbors or background may or may not be sufficient to identify the object. 

The stepped-FM UWB sensor can detect radio interference by monitoring the phase detector output in passive mode (transmitter power off/receiver on) and is then designed to have some spectrum hole (nonactivated within a portion of the wide radio spectrum) at the transmitter in order to prevent any conflict and to coexist with the other narrow-band wireless systems. Note that the transmit radio consists of independent narrow-band pulses with a different frequency. As such, if provides the flexibility to support... 

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