Differences

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--- instruments:tsi:tsi [2021/01/22 21:17] – external edit 127.0.0.1
+++ instruments:tsi:tsi [2024/07/02 14:38] (current) – [Principle] jan
@@ Line 11: / Line 11: @@
 Channels are in the visible range with average wavelengths of ~650nm (red), ~510nm (green), ~465nm (blue), have a broad spectral sensitivity and do overlap. Peak sensitivity wavelengths are at 560nm (red), 530nm (green) and 430nm (blue) (at least these are the peak sensitivities of our visual system which a camera tries to mimic). But unfortunately the system is not calibrated: the camera adapts its exposure to received light (i.e. sensitivity changes in time). White balance is set to a constant value to ensure that sensitivity of the channels relative to each other is constant. Every 15minutes is varied exposure (collecting time of the sensor) and gain (amplifier within the sensor) which might be used to derive an absolute calibration.
+The camera follows the equisolid model, that means that every pixel receives radiation from solid angles of the same size. That means radius $R$ in the image relative to radius of the horizon $R_0$ follows roughly the sine of the half zenith angle $\theta$, i.e. $ R = R_0 \cdot \sin(\theta/2) $.
 The camera replaced a [[instruments:tsi:yes-tsi|YES total sky imager]] which died after some years of operation.