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Enabling better global research outcomes in soil, plant & environmental monitoring.


The SNiP-SQF is a 'Sensor Node Integrated Package' for LoRaWAN or CAT-M1 communication of real-time measurements of photons spread out in a particular area, for continuous plant, light and environmental monitoring.


The base SNiP-SQF integrates 1x S-NODE and 1x SQ-521 PAR Sensor to a site’s unique network, communication and power requirements. The S-NODE can support an additional 3 sensors.

The SQ-521 PAR Sensor is a digital sensor with SDI-12 communication protocol. Typical applications include PPFD measurement over plant canopies in outdoor environments, greenhouses, and growth chambers, and reflected or under-canopy (transmitted) PPFD measurements in the same environments. Quantum sensors are also used to measure PAR/PPFD in aquatic environments, including salt water aquariums where corals are grown.


See Further Specifications on the S-NODE
See Further Specifications on the SQ-521 PAR Sensor

Further parameters can be added to the SNiP, without requiring loggers to match each distinct sensor, substantially reducing the cost of getting a fuller picture on the application.

Radiation that drives photosynthesis is called photosynthetically active radiation (PAR) and is typically defined as total radiation across a range of 400 to 700 nm. PAR is often expressed as photosynthetic photon flux density (PPFD): photon flux in units of micromoles per square meter per second (μmol m-2 s-1, equal to microEinsteins per square meter per second) summed from 400 to 700 nm (total number of photons from 400 to 700 nm). While Einsteins and micromoles are equal (one Einstein = one mole of photons), the Einstein is not an SI unit, so expressing PPFD as μmol m-2 s-1 is preferred.

The acronym PPF is also widely used and refers to the photosynthetic photon flux. The acronyms PPF and PPFD refer to the same parameter. The two terms have co-evolved because there is not a universal definition of the term “flux”. Some physicists define flux as per unit area per unit time. Others define flux only as per unit time. We have used PPFD in this manual because we feel that it is better to be more complete and possibly redundant.

Sensors that measure PPFD are often called quantum sensors due to the quantised nature of radiation. A quantum refers to the minimum quantity of radiation, one photon, involved in physical interactions (e.g., absorption by photosynthetic pigments). In other words, one photon is a single quantum of radiation.

Typical applications of quantum sensors include incoming PPFD measurement over plant canopies in outdoor environments or in greenhouses and growth chambers, and reflected or under-canopy (transmitted) PPFD measurement in the same environments.

Apogee Instruments SQ series quantum sensors consist of a cast acrylic diffuser (filter), photodiode, and signal processing circuitry mounted in an anodised aluminium housing, and a cable to connect the sensor to a measurement device. SQ-500 series quantum sensors are designed for continuous PPFD measurement in indoor or outdoor environments. The SQ-521 sensors output a digital signal using SDI-12 communication protocol.


The S-NODE (for Environmental Monitoring) has been designed to support the broad suite of SDI-12 based environmental sensors. The S-NODE can support sensors with higher power requirements; a solar panel can charge either the internal lithium-ion battery or both the node and sensor can be powered by an external 12V system (e.g. battery or mains source).

A decoder suitable for TTN will be provided based upon sensor configuration.

  • LoRaWAN™ low-power long-range connectivity
  • Supports the full range of SDI-12 commands, and sensors requiring constant excitation.
  • Optional CAT-M1
  • Solar rechargeable Lithium-ion or external 12V power options
  • Optional Multi-constellation GNSS
  • AS923, AU915 and US915 available, with other region plans available upon request.
  • Standard IP65 enclosure, optional IP67

SQ-521 PAR Sensor

Input Voltage Requirement: 4.5 to 24V DC
Current Drain: 0.6 mA (quiescent), 1.3 mA (active)
Calibration Uncertainty: ± 5%
Measurement Repeatability: Less than 1% (up to 4000 µmol mˉ² sˉ¹)
Non-stability (Long-term Drift): Less than 2% per year
Non-linearity: Less than 1% (up to 4000 µmol mˉ² sˉ¹)
Response Time: 0.6 s, time for detector signal to reach 95% following a step change, fastest data transmission rate for SDI-12 circuitry is 1s
Field of View: 180˚
Spectral Range: 389 to 692 nm ± 5 nm (wavelengths where response is greater than 50% of maximum)
Spectral Selectivity: Less than 10% from 412 to 682 nm ±5 nm
Directional (Cosine) Response: ±2% at 45˚, ±5% at 75˚
Azimuth Error: Less than 0.5%
Tilt Error: Less than 0.5%
Temperature Response: -0.11 ±0.04% per °C
Uncertainty in Daily Total: Less than 5%
Detector: Blue-enhanced silicon photodiode
Housing: Anodised aluminium body with acrylic diffuser
IP Rating: IP68
Operating Environment: -40 to 70°C, 0 to 100% relative humidity, can be submerged in water up to depths of 30 m
Dimensions: 45 mm height, 23.5 mm diameter
Mass: 100 g
Cable: 5 m of two conductor, shielded, twisted-pair wire; additional cable available in multiples of 5 m; santoprene rubber jacket; pigtail lead wires