SPECTROSCOPY


something less than that. Te Ocean SR2 outperforms a comparable spectrometer for absorbance measurements, especially in the UV. Tis is an appealing feature for applications such as molecular diagnostics. SNR is the signal intensity divided


by the noise intensity at a certain signal level, which means SNR can vary from measurement to measurement. Since system noise typically increases as a function of signal due to photon noise, the SNR function is a plot of individual SNR values versus the signal at which they were obtained. Some manufacturers report spectrometer SNR as the maximum possible SNR value obtained at detector saturation. Te SNR response curve for each pixel is assumed to be the same. SNR can be improved by signal


averaging, as was done for most of the measurements here. For time-based averaging, the SNR will increase by the square root of the number of spectral scans used. For example, an SNR of 380:1 will become 3800:1 if 100 scans are averaged. For spatially based averaging (boxcar), the SNR will increase by the square root of the number of pixels averaged.


Fig. 2.


In these measurements, the vertical lines represent calibrated absorbance wavelengths at 235nm, 257nm, 313nm, 350nm and 430nm


Rob Morris is with Ocean Insight www.oceaninsight.com


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