Comparison of COSPEC and two miniature ultraviolet spectrometer systems for SO₂ measurements using scattered sunlight

The correlation spectrometer (COSPEC), the principal tool for remote measurements of volcanic SO₂, is rapidly being replaced by low-cost, miniature, ultraviolet (UV) spectrometers. We compared two of these new systems with a COSPEC by measuring SO₂ column amounts at Kīlauea Volcano, Hawaii. The two systems, one calibrated using in-situ SO₂ cells, and the other using a calibrated laboratory reference spectrum, employ similar spectrometer hardware, but different foreoptics and spectral retrieval algorithms. Accuracy, signal-to-noise, retrieval parameters, and precision were investigated for the two configurations of new miniature spectrometer. Measurements included traverses beneath the plumes from the summit and east rift zone of Kīlauea, and testing with calibration cells of known SO₂ concentration. The results obtained from the different methods were consistent with each other, with