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In astrophysics and planetary science, spectral slope, also called spectral gradient , is a measure of dependence of the reflectance on the wavelength. In digital signal processing, it is a measure of how quickly the spectrum of an audio sound tails off towards the high frequencies, calculated using a linear regression.〔G. Peeters, (A large set of audio features for sound description ), tech. rep., IRCAM, 2004.〕 ==Spectral slope in Astrophysics / Planetary Science== The visible and infrared spectrum of the reflected sunlight is used to infer physical and chemical properties of the surface of a body. Some objects are brighter (reflect more) in longer wavelengths (red). Consequently, in visible light they will appear redder than objects showing no dependence of reflectance on the wavelength. The diagram illustrates three slopes: *a ''red slope'', the reflectance is increasing with the wavelengths *''flat spectrum'' (in black) *And a ''blue slope'', the reflectance actually diminishing with the wavelengths The slope (spectral gradient) is defined as: : :where is the reflectance measured with filters F0, F1 having the central wavelengths λ0 and λ1, respectively.〔 〕 The slope is typically expressed in percentage increase of reflectance (i.e. reflexivity) per unit of wavelength: %/100 nm (or % /1000 Å) The slope is mostly used in near infrared part of the spectrum while colour indices are commonly used in the visible part of the spectrum. The trans-Neptunian object Sedna is a typical example of a body showing a steep red slope (20%/100 nm) while Orcus' spectrum appears flat in near infra-red. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spectral slope」の詳細全文を読む スポンサード リンク
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