Key Operations: Prior to each field campaign, a comprehensive inspection of the spectroradiometer mainframe, fiber optic probe, reference white panel, and batteries must be performed. Verify that the fiber optic cable is free from excessive bending (bending radius ≥ 15cm), the probe lens is clean and unobstructed by smudges, and the white panel surface is free from scratches or contaminants. Warm-up Specifications: Upon powering on, the spectroradiometer should be placed in a stable environment to warm up for at least 15-20 minutes, ensuring the detector reaches thermal equilibrium. During warm-up, avoid exposing the instrument to direct sunlight and deactivate unnecessary high-power modules. Once the warm-up is complete, perform a dark current acquisition and white panel calibration to verify baseline stability. Logging Requirements: Document the instrument model, warm-up start and end times, ambient temperature, battery level, and reference panel serial number in the field data log to facilitate post-processing traceability and quality assessment.

Site Requirements: Select homogeneous, representative target areas for target measurement, avoiding boundary transition zones. Ensure that the measurement area is completely free from shadows (including those cast by the operators themselves) and is situated away from high-reflection interference sources such as tall buildings or bodies of water. Time Window: The recommended time window for field measurements is between 10:00-14:00 local time, when the solar zenith angle is minimal (solar altitude angle > 45°), ensuring that diurnal solar irradiance peaks and varies relatively smoothly. Avoid operations under overcast skies, hazy conditions, damp ground post-rain, or when wind speeds exceed 5m/s. Incident Light Monitoring: Utilize a spectral irradiance meter to log ambient light variations every 15 minutes. If the fluctuation in incident light intensity between two consecutive measurements exceeds ± 5%, the reference white panel must be recalibrated, and the affected sample points must be flagged.

Panel Optimization: Only use traceable and calibrated high-reflectance diffuse panels (typically composed of Spectralon material) with a nominal reflectance value above 95%. When positioning the white panel, maintain the identical height and inclination angle as the target surface, and ensure that fingers do not obstruct the panel nor dust accumulates on its surface. Calibration Frequency: Adopt the "Dual-Frequency Calibration Method"—re-measure the reference white panel immediately after measuring every 5-10 targets. If ambient light changes rapidly (due to passing clouds or fast-shifting solar angles), shorten the interval to every 3-5 sample points. Each measurement sequence must begin and end with reference white panel acquisitions. Panel Maintenance: Before and after each field campaign, clean the panel surface using a dedicated soft-bristle brush or dry compressed nitrogen gas. Never touch the surface with bare hands or wipe it with liquid solvents. The panel must be stored in its specialized dust-proof case to avoid scratches and chemical contamination, and should be sent for annual reflectance recalibration.

Measurement Geometry: The angle between the fiber optic probe normal and the target surface normal must be ≤ 10° (nadir measurement). Calculate the distance between the probe and the target surface based on the Field of View (FOV) to ensure that the field-of-view footprint falls entirely within the target boundary. A distance of 0.3-0.5 meters is recommended (corresponding to a footprint diameter of approximately 13-22cm at a 25° FOV). Sampling Strategy: For each sample point, repeat the measurement 5-10 times, discard obvious outliers, and compute the arithmetic mean. For heterogeneous targets (e.g., sparse vegetation, patchy terrain), distribute multiple sub-sampling points (no less than 3) evenly within the plot to compute both the mean and standard deviation. Operator Posture: Operators must stand facing away from the sun to prevent their body or clothing from obstructing or reflecting stray light onto the target. Maintain fiber optic stability during measurements to eliminate shaking. Extension poles or tripods can be used to secure the probe and minimize manual jitter.

In Situ Logging: Utilize standardized field datasheets (hardcopy or digital tablet) to record: sample point ID, GPS coordinates, acquisition time, weather conditions, illumination states, target descriptions, operator names, instrument metadata (integration time, averaging configurations), and relevant remarks. Data Storage: Export raw spectral files immediately upon completing measurements, utilizing a standardized naming convention of "YYYYMMDD + Location + Sample_ID". Back up files to at least two independent storage media (e.g., local hard drive + cloud storage) and perform a preliminary data quality check on the same day (reviewing curve profiles for anomalous steps or instrument noise). Daily Maintenance: Following each field operation, use specialized cleaning tools to remove dust and debris from the fiber optic probe and instrument chassis. Inspect the fiber optic end-face and SMA connectors for contamination or abrasions. Once fully charged, disconnect the power supply and store the equipment in a desiccator cabinet (relative humidity < 60%). Perform wavelength and radiometric calibrations quarterly to guarantee long-term measurement precision.

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