## 1 Introduction  
Remote sensing reflectance (sr\({}^{-1}\)) of water bodies is an important apparent optical quantity that can be detected in water color remote sensing and is one of the important parameters to quantify the spectral information of water bodies [1]. The field measurement of water remote sensing reflectance is a key step in the remote sensing of water color, and is widely used in the research and commercialization of satellite authenticity verification, water quality parameter inversion [2], cyanobacterial bloom [3] and black-odor water body identification [4]. The remote sensing of water color can be divided into the remote sensing of marine water bodies and the remote sensing of inland water bodies, with the remote sensing of marine water bodies being utilized to mainly observe the surface chlorophyll-a (Chl-a) concentration [5], suspended particular matter (SPM) concentration [6] and colored dissolved organic matter (CDOM) [7]. The remote sensing of inland water bodies has been used to estimate, in addition to the parameters mentioned above, total phosphorus (TP), total nitrogen (TN), the trophic state index (TSI) and, more recently, dissolved organic carbon in an eutrophic lake [8] and methane emissions in a lake [9]. Current spectrometers dedicated to R_rs_ based on water bodies include the Analytical Spectral Devices (ASD) series from Malvern Panalytical in the UK [10], the Profiling Reflectance Radiometer (PRR) series from Biospherical in the USA [11], the PAMSES series from Trios in Germany [12] and the Satlantic series from a subsidiary of SeaBird in the USA [13]. Measuring the R_rs_ is an essential step in both marine remote sensing and inland water remote sensing. In oceanic remote sensing, the spectrometer is mainly carried on board a research vessel for walk-around measurements, and the same method is applied in inland lakes. There is a great deal of preparation before the measurement is carried out: firstly, the spectrometer is charged; secondly, the instruments are inventoried for transport; and finally, the spectrometer is deployed on board the research vessel. All of the above spectrometers can be utilized for the measurement of parameters in water bodies. However, they all are of a large size and weight and require a power supply, and thus, we cannot bring the spectrometer to lakes or rivers in unmanned areas such as the Tibetan Plateau. Therefore, there has been a gap in our knowledge on the water spectra of lakes or rivers in unmanned areas of the Tibetan Plateau. Furthermore, in inland water environments there are often unpopulated waters and waters that cannot be measured by using large vessels, and the above-mentioned water body R_rs_ cannot be measured. Micro-spectrometers have the advantage of being small in size [14], and instead of spectrometers, they have been carried on board unmanned aerial vehicles or unmanned ships for R_rs_ measurements to solve these problems. Nowadays, scholars often use imaging spectrometers for spectrometric measurements via unmanned aerial vehicles, and there are empirical linear-based [15] and look-up table methods [16] for radiometric calibrations of imaging spectrometers. The main applications are in vegetation and crop studies [17], and scholars have also used them to perform techniques for estimating water quality parameters [18; 19]. However, imaging spectrometers tend to have a low signal-to-noise ratio for measuring the remote sensing spectra of water bodies. However, none of the current commercial micro-spectrometers are radiometrically calibrated; thus, we need to carry out a radiometric calibration of the micro-spectrometer. The radiometric calibration of the micro-spectrometer can be performed by using a high-precision spectrometer and a micro-spectrometer to simultaneously measure high-precision stable irradiance and irradiance sources and to solve for the conversion relationship between the digital number (DN) recorded by the micro-spectrometer and the radiance and irradiance values received by the micro-spectrometer.