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I'm a bit confused between two units for spectral irradiance, specifically $W/sr/m^2/nm$ and $\mu Jy/"^2$, which is analogous to $W/sr/m^2/Hz$.

It seems to me that I need some sort of spectral bandwidth, but I don't get which one to use in the case of hyperspectral data.

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  • $\begingroup$ Spectral quantities can be expressed in terms of either frequency or wavelength. Take your pick. en.wikipedia.org/wiki/Radiance $\endgroup$ – G. Smith Aug 14 at 22:03
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    $\begingroup$ The relationship is $L_\nu\,d\nu=L_\lambda\,d\lambda$. $\endgroup$ – G. Smith Aug 14 at 22:08
  • $\begingroup$ Sure, but what number is that? Do I directly use $\nu$ and $\lambda$ or do I need to integrate somehow? $\endgroup$ – asimoneau Aug 14 at 22:13
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    $\begingroup$ $d\nu/d\lambda$ or $d\lambda/d\nu$ is not a number. They are functions of $\nu$ or $\lambda$ which follow from $\lambda\nu=c$. So there is not a single conversion factor between the units. The factor depends on the frequency or the wavelength. $\endgroup$ – G. Smith Aug 14 at 22:21
  • $\begingroup$ Alright, I think I'm getting it. So the factor $d\nu/d\lambda$ is about equal to $c/\lambda^2$ ? $\endgroup$ – asimoneau Aug 14 at 22:26

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