Handheld spectroradiometer, as a key tool for quickly obtaining the spectral reflectance, emissivity or transmittance of objects, is widely used in remote sensing surveying, agricultural production, cultural relic protection and other fields. However, its measurement results are susceptible to multiple factors, and if not controlled, it may lead to data bias or even failure. The following analysis will be conducted from four aspects: instrument characteristics, environmental conditions, operating standards, and properties of the tested object.
1、 Performance limitations of the instrument itself
The hardware configuration of the device directly determines the basic accuracy. Firstly, the sensitivity of the detector is negatively correlated with spectral resolution - in high-resolution mode, the slit of the monochromator becomes narrower, which can distinguish finer wavelength differences, but reduces the number of photons received per unit time, resulting in a decrease in signal-to-noise ratio, especially in low light environments; On the contrary, although the low resolution mode improves the signal-to-noise ratio, it may lose the detailed information of adjacent bands. Secondly, the accuracy of the built-in calibration module is crucial. Most instruments use standard whiteboards for factory calibration, but as the frequency of use increases, the surface of optical components may adsorb dust or age, causing a deviation in the reference value. It is necessary to regularly recalibrate with a standard board with known diffuse reflectance. In addition, when the battery is low, unstable circuit power supply may cause data acquisition interruption or numerical jump.
2、 Dynamic interference of environmental conditions
Changes in the natural environment significantly affect measurement stability. Light intensity is the core variable: direct exposure to strong light can saturate the detector, especially in the UV visible wavelength range, and the superposition of stray light can easily cause "spillover effects"; On cloudy or shaded areas, the signal-to-noise ratio is reduced due to insufficient incident energy. The environmental temperature and humidity act in two ways: high temperature accelerates the thermal noise of electronic devices, while also promoting the evaporation of surface moisture on the sample to change its physical properties; In high humidity environments, condensation of water vapor on the instrument window scatters light, and humid air enhances absorption of the infrared band. Wind speed disturbance cannot be ignored, as the instantaneous airflow during measurement drives the displacement of blades or powdered samples, resulting in changes in the effective detection area and an increase in data dispersion during repeated measurements.
3、 Human error in the operation process
The user's operating habits profoundly shape the final result. The control of measuring distance and angle is the most critical: non-contact measurement relies on geometric relationships. If the distance is too close and exceeds the depth of field range, the image will be blurred, while if it is too far, the inverse square law error will be introduced due to light intensity attenuation; When the tilt angle deviates from the normal direction, the proportion of specular reflection components increases sharply, which breaks the assumption of uniform sampling under the Lambertian assumption. The integration time setting needs to balance response speed and signal accumulation. It is suitable for bright scenes in the short term, and although it can capture dark details in the long term, the small displacement caused by mechanical vibration will be amplified as stripe noise. The micrometer level displacement generated by handheld shaking can cause a relative error of 5% -10% in micro area measurement.
4、 The complex characteristics of the tested object
The physical and chemical properties of the sample itself pose a fundamental challenge. Surface roughness determines whether diffuse reflection dominates or specular reflection takes priority. Polished metal exhibits sharp peaks, while frosted materials form a wide distribution. The depth of color directly affects the absorption ratio of each band. Dark objects have low reflectivity in the visible light region, but may produce characteristic peaks in the near-infrared region due to molecular vibrations. The interlayer refractive index difference of multi-layer structural materials causes multiple internal reflections, making it difficult for conventional models to accurately analyze real spectra. The moisture content of biological samples dynamically changes over time, and the chlorophyll content fluctuates day and night, requiring real-time synchronous recording of environmental parameters.
The reliability of the results of a handheld spectroradiometer depends on the coordinated control of instrument performance, environmental adaptation, operating standards, and sample characteristics. In practical applications, a standardized process needs to be established, combined with multiple repeated measurements and cross validation, in order to maximize the approximation of true spectral features.