Measurement Error Analysis of Seawater Refractive Index: A Measurement Sensor Based on a Position-Sensitive Detector

Area of Science:

• Oceanography
• Optical Physics
• Metrology

Background:

• Accurate seawater refractive index measurement is vital for ocean observation.
• Position-sensitive detector (PSD) systems offer high-precision measurement capabilities.
• Jitter signal errors can significantly impact the accuracy of refractive index measurements.

Purpose of the Study:

• To theoretically analyze the causes of jitter signals in seawater refractive index measurements.
• To identify and quantify factors affecting PSD measurement accuracy.
• To develop and validate an optimized system for reducing measurement errors.

Main Methods:

• Theoretical analysis of jitter signal causes, focusing on window angles and PSD influencing factors.
• Implementation of a narrow-band filter (0.9 nm bandwidth) to mitigate background light.
• Selection of a 4 mm × 4 mm PSD and partitioning of the measurement system to control temperature variations.
• Experimental validation using standard seawater samples to assess system optimization.

Main Results:

• Identified window angle as a key error source, reducible by maintaining angles within 2.06°.
• Quantified the negative impact of background light, PSD photosensitive surface size, and temperature fluctuations.
• Optimized system reduced jitter signal from 0.0022 mm to 0.0011 mm.
• Demonstrated a significant reduction in refractive index deviation post-optimization.

Conclusions:

• Optimizing the optical path and structural design of PSD-based systems effectively reduces jitter signals.
• Controlled window angles, filtered light, appropriate PSD selection, and stable temperature are critical for accurate seawater refractive index measurement.
• The optimized system significantly enhances the precision of seawater refractive index determination for oceanographic applications.