This child data release includes field spectra and in situ measurements of Rhodamine WT dye concentration acquired during a tracer experiment performed on the Missouri River near Columbia, Missouri, on May 5, 2021. One of the primary goals of this tracer experiment was to assess the feasibility of inferring concentrations of a visible dye (Rhodamine WT) from various types of remotely sensed data in a large, highly turbid natural river channel. Previous research on remote sensing of tracer dye concentrations has focused on clear-flowing streams, but the Missouri River is much more turbid. As a result, the effect of the dye on the reflectance of the water could be obscured by the effects of suspended sediment on reflectance. This experiment thus provided an initial test of the potential to map dye concentrations from remotely sensed data in more turbid rivers like the Missouri. The experiment involved introducing a pulse of Rhodamine WT dye into the channel at an upstream transect and then observing the dispersion of the dye along the river using various in situ and remote sensing instruments. For example, field spectra were used to quantify the reflectance characteristics of the water as the dye concentration varied over the course of the experiment. An ASD HandHeld2 Pro spectroradiometer deployed from a boat was used to record field spectra from above the water surface in reflectance mode, with periodic measurements from a Spectralon panel serving as the white reference. A separate set of of field spectra was collected on each traverse of a channel cross-section. Data from four such transects, each spanning about ten minutes in time, is included in this data release. Each spectrum was subjected to a third-order Savitzky-Golay smoothing filter applied twice over a 15 nm window and then subset to the wavelength range from 400-900 nm.
In addition to the spectra, a Trimble Geo7X handheld GPS receiver was used to record spatial coordinates as the boat traversed the channel and a Turner C3 submersible fluorometer (sonde) was used to measure the Rhodamine WT dye concentration in parts per billion (ppb). The dye concentration at each spectral measurement location was interpolated in time based on the sonde data by pairing time stamps from the spectra with those from the sonde. This data release provides both the reflectance spectra and the interpolated dye concentrations, as well as locations and time stamps, and can be used to develop relationships between concentration and reflectance for mapping dye dispersion in river channels from field spectra or passive optical remotely sensed data. The field spectra from throughout the experiment are compiled in a single file, MissouriDyeFieldSpectra.csv, and organized by cross-section number. The file also includes columns for the UTC time of the spectrum, the easting and northing spatial coordinates (UTM Zone 15S, NAD83), and the interpolated dye concentration in ppb. The remaining columns are for the reflectance at each wavelength from 400-900 nm in 1 nm increments.