Kipp&Zonen SGR3 Longwave Radiometer

Overview

The Kipp&Zonen SGR3 Longwave Radiometer is a precision thermopile-based instrument engineered to measure downward longwave (infrared) radiation in the spectral range of 4.5–42 µm. It operates on the principle of net radiative heat exchange between the sensor’s blackened thermopile detector and the hemispherical sky dome, generating a voltage output proportional to the incident radiant flux. Unlike shortwave radiation (300–4000 nm), which originates primarily from solar emission, longwave radiation is emitted by the Earth’s surface and atmospheric constituents—including clouds, water vapor, CO₂, and aerosols—following absorption and thermal re-emission. Accurate quantification of this component is essential for surface energy balance studies, climate modeling, evapotranspiration estimation, and performance validation of photovoltaic power plants. The SGR3 delivers calibrated, temperature-compensated output under varying ambient conditions, supporting continuous, unattended operation in field-deployed meteorological networks and solar resource assessment campaigns.

Key Features

• Thermopile detector with spectrally flat response across 4.5–42 µm, coated with high-absorptance black paint and protected by a silicon dome optimized for infrared transmission
• Integrated Pt100 temperature sensor for real-time instrument body temperature measurement—critical for accurate longwave flux correction per ISO 9060:2018 Class C specifications
• Modbus® RTU over RS-485 interface enabling direct integration into SCADA, PLC, and data logger systems without external signal conditioning
• Dual analog outputs (0–1 V and 0–5 V) with improved linearity and reduced thermal drift compared to legacy SGR models
• Enhanced temporal response: <1 s (95% response time) under standard conditions, minimizing lag during rapid cloud transients
• Wide DC power supply range (5–30 VDC), compatible with battery-, solar-, or grid-powered remote stations
• Robust aluminum housing with IP67-rated waterproof connector (M12 type), facilitating field maintenance, recalibration, and sensor replacement without tools
• Integrated bubble level and adjustable leveling feet ensure precise horizontal alignment—essential for cosine-corrected irradiance measurements
• Five-year manufacturer warranty reflecting structural durability and long-term calibration stability

Sample Compatibility & Compliance

The SGR3 is designed for outdoor deployment in open-sky configurations and may be mounted on meteorological masts, solar tracking platforms, or agricultural weather stations. It complies with the spectral and directional requirements defined in ISO 9060:2018 (Class C) for pyrgeometers and meets the environmental robustness criteria outlined in IEC 61215-2 (for PV monitoring applications). While not intrinsically certified for hazardous locations, its enclosure satisfies EN 60529 (IP67) for dust and water ingress protection. Data acquisition workflows using the SGR3 support traceable calibration chains aligned with WMO Guide to Instruments and Methods of Observation (CIMO Guide, Chapter 8) and are suitable for use in GLP-compliant environmental monitoring programs where audit-ready metadata logging is required.

Software & Data Management

The SGR3 ships with SmartExplorer™ for Windows—a vendor-provided configuration and visualization utility supporting real-time Modbus register mapping, firmware updates, and diagnostic status checks. Users can define custom scaling factors, configure polling intervals, and export time-synchronized datasets (detector voltage + body temperature) in CSV or ASCII format. When integrated with third-party data loggers (e.g., Campbell Scientific CR series, Delta-T DL6), the SGR3 supports timestamped, dual-channel recording compliant with FAO-56 evapotranspiration protocols and BSRN (Baseline Surface Radiation Network) metadata standards. All Modbus registers adhere to standard function codes (0x03, 0x06), enabling interoperability with Python-based telemetry frameworks (e.g., pymodbus) and MATLAB Instrument Control Toolbox deployments.

Applications

• Surface energy balance closure studies in eddy covariance flux towers
• Downward longwave irradiance input for PV system performance ratio (PR) analysis per IEC 61724-1
• Validation of numerical weather prediction (NWP) model output for cloud radiative forcing
• Soil-plant-atmosphere continuum (SPAC) modeling in precision agriculture
• Long-term climate observatories requiring multi-decadal radiometric consistency
• Calibration transfer and intercomparison campaigns within BSRN or GCOS reference sites

FAQ

What is the recommended calibration interval for the SGR3?
Kipp&Zonen recommends recalibration every two years under normal operational conditions; annual calibration is advised for installations in high-dust, coastal, or high-UV environments.
Does the SGR3 require a separate ventilator or heater?
No—the SGR3 is a passive, non-ventilated pyrgeometer. Its design relies on thermal equilibrium and built-in temperature compensation rather than active heating or forced airflow.
Can the SGR3 be used to measure upward longwave radiation?
Yes—when inverted and mounted over a reflective surface (e.g., aluminum foil or white diffuser), the SGR3 measures upward longwave flux; however, directional cosine errors increase beyond ±60° zenith angle.
Is the Modbus address configurable?
Yes—device ID, baud rate, parity, and stop bits are fully programmable via SmartExplorer™ or direct Modbus write commands to holding registers.
How is thermal offset corrected in post-processing?
The instrument outputs both raw thermopile voltage (V_det) and body temperature (T_body). Downward longwave irradiance (L↓) is calculated as: L↓ = V_det/S + σ·T_body⁴, where S is the calibration sensitivity (W·m⁻²·V⁻¹) and σ is the Stefan–Boltzmann constant.