![]() ![]() ![]() Extreme UV and X-rays are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power. The optical atmospheric window Solar irradiance spectrum above atmosphere and at surface. Disambiguation of the term 'optical spectrum' Īlthough the word optical, deriving from Ancient Greek ὀπτῐκός (optikós, “of or for sight”), generally refers to something visible or visual, the term optical spectrum is used to describe the sum of the visible, the ultraviolet and the infrared spectra (at least in this context). The earth's atmosphere is not totally transparent and is in fact 100% opaque to many wavelengths (see plot of Earth's opacity) the wavelength ranges to which it is transparent are called atmospheric windows. ![]() Sunlight mostly reaches the ground through the optical atmospheric window the sun is particularly active in most of this range (44% of the radiation emitted by the sun falls within the visible spectrum and 49% falls within the infrared spectrum). The window runs from around 300 nanometers ( ultraviolet-B) up into the range the human eye can detect, roughly 400–700 nm and continues up to approximately 2 μm. The optical window is a range of wavelengths that are not blocked by the earth's atmosphere. Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light. Unsourced material may be challenged and removed.For the optical element, see Window (optics). Please help improve this section by adding citations to reliable sources. Other definitions of SNR may use different factors or bases for the logarithm, depending on the context and application. The most common way to express SNR is in decibels, which is a logarithmic scale that makes it easier to compare large or small values. SNR can be calculated using different formulas depending on how the signal and noise are measured and defined. This relationship is described by the Shannon–Hartley theorem, which is a fundamental law of information theory. SNR also determines the maximum possible amount of data that can be transmitted reliably over a given channel, which depends on its bandwidth and SNR. SNR can be improved by various methods, such as increasing the signal strength, reducing the noise level, filtering out unwanted noise, or using error correction techniques. A high SNR means that the signal is clear and easy to detect or interpret, while a low SNR means that the signal is corrupted or obscured by noise and may be difficult to distinguish or recover. SNR is an important parameter that affects the performance and quality of systems that process or transmit signals, such as communication systems, audio systems, radar systems, imaging systems, and data acquisition systems. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise. SNR is defined as the ratio of signal power to noise power, often expressed in decibels. Signal-to-noise ratio ( SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. Not to be confused with Signal-to-interference-plus-noise ratio. ![]()
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