The Importance of Dynamic Range and Signal to Noise Ratio in Spectrometers
Spectrometer performance standards can be difficult to explain, although common vocabulary can help. In this technical tip, we considered two important but often misunderstood terms: dynamic range and signal-to-noise ratio.
Spectroscopy is a complex technique that needs to consider many changes and nuances, usually framed by terms that are unfamiliar to users or terms that can be explained in different ways. In this context, we have provided some practical definitions of dynamic range and signal-to-noise ratio (SNR), which are generally considered to be common measures of spectrometer performance.
In spectroscopy, dynamic range is the ratio between the maximum peak height signal intensities and readout noise ( no peak area ) that a spectrometer can detect. More specifically, dynamic range is the maximum detectable signal (i.e., near saturation) divided by the minimum detectable signal. The minimum detectable signal is defined as the signal with an average equal to the baseline noise.
For our spectrometers, Optosky reports dynamic range in terms of a single acquisition, which is defined as the shortest integration time giving the highest possible dynamic range. The dynamic range specification of the system as a whole is defined as the product of the ratio of maximum to minimum signal at the longest integration time and the ratio of the maximum to minimum integration time.
Signal to Noise Ratio (SNR)
Signal to noise ratio (SNR) is defined as the signal intensity divided by the noise intensity at a certain signal level, which means it 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. The value of a spectrometer’s SNR reported by Optosky is the maximum possible SNR value (obtained at detector saturation). The SNR response curve for each pixel is assumed to be the same.
The SNR measurement is performed as follows: Set the integration time of the spectrometer according to the light intensity to make the spectrum reach 80% of the full scale position; set the accumulation times to 1, and the sampling interval to 0.1s. Collect the spectrum signal 10 times continuously. Calculate the signal-to-noise ratio of the spectrometer according to formulas (6) and (7):
Sλ-the standard deviation of n measurements at the wavelength λ;
Aλi-the value of the i-th measurement at the wavelength λ;
Aλ-the average value of n measurements at the wavelength λ;
n—Number of measurements.
Several Other Avenues to Improve SNR
- Increase the light source output.
- Use a large-diameter fiber for transferring the light to the sample, to capture more light from the source.
- Increase the integration time of the detector.
- Limit the incoming lamp spectrum to only the wavelength span of interest, using the full dynamic range of the detector in the region where it matters most. This is especially true for the edges of the spectrum, which often suffer from lower intensities.
Overview of Spectrometers by Dynamic Range and Signal to Noise Ratio
Here’s an overview of Optosky spectrometers by detector type, dynamic range and SNR. While these criteria can offer some insight into the suitability of a particular spectrometer model for an application, there are many other factors that go into spectrometer selection. Optosky can provide guidance.
|ATP1010||Microspectrometers||Hamamtsu S13014 Linear CMOS||10000：1||> 450:1|
High-intensity laser analysis
Integration into other devices
|ATP2000P||General Purpose||Hamamtsu S11639 Linear COMS||5000||>600 : 1||Basic lab measurements|
|ATP3330||Ultra-high Resolution||Linear array detector||8.5 x 107 (system); 2000:1 for a single acquisition||>600:1|
Emission line analysis
Hamamtsu S16011 TE-cooled
(cooling to -10ºC)
Low light level fluorescence and Raman
Analysis of solutions, solids and gases
back-thinned linear CCD
(cooled down to -20ºC)
Low light applications including:
|ATP8600||NIR (900-1700 nm)||Uncooled InGaAs linear array||14667||>2255:1|
Food composition analysis
|ATP8000||NIR (900-2500 nm)||Cooled Linear InGaAs CCD, |
Cooled down to -20ºC