The measurement of particle plume and curtain temperatures in particle-laden gravity-driven flows presents a unique challenge to thermometry due to the flow’s transient and stochastic nature. Earlier attempts to assess the bulk particle temperature of a plume using intrusive and non-intrusive methods have produced very limited success. Here we describe a non-intrusive method using a high-speed IR camera (ImageI8300 from Infratec) and a visible-light camera (Nikon D3500) to produce indirect particle temperature measurements. The IR camera produces thermogram sets mapping the apparent particle temperature, while the visible-light image sets allow for the calculation of the plume opacity as a function of flow discharge position. An in-house post-processing algorithm based on Planck’s radiation theory was developed to compute the true particle temperature which is a function of the apparent temperature (thermograms) and the plume opacity obtained from the visible-light images. To validate these results, a series of lab-scale tests generating particle curtains of known dimensions at various temperatures were performed. The lab-scale tests were conducted using a small particle receiver which is equipped with thermocouples to measure the temperature directly. Using the recorded thermocouple data, a particle temperature function can be derived empirically, based on the lumped capacitance model for a free-falling sphere. The empirical particle temperature function is then compared with the temperature data measured using the methodology outlined in this work yielding agreement of the bulk particle temperature of the plume. The methods described here will be developed further to estimate the heat losses from the falling particle receiver at Sandia National Labs.