The total noise in the sensor is the sum of the photon noise (shot noise), the dark noise, the readout noise, and the digitization noise. The photon noise arises due to variations in the number of photons that are detected by the sensor per unit time.
The signal-to-noise ratio is, SNR= Incoming Signal/noise
There are many studies which showed that low SNR affect the estimation of some parameters such as using HICO hyperspectral image to estimate Chlorophyll-a and other parameters. The study (see reference below) showed that variations up to 80% were observed in the estimated Chlorophyll-a concentration due to photon noise.