By Kestrel

Kestrel 3550AG Pocket Delta T Crop Spraying Weather Meter

Avoid spray drift with this portable, connected handheld weather meter

Regular price $229.00 USD
Regular price $289.00 USD Sale price $229.00 USD
Shipping calculated at checkout - Free in the USA.
Availability: In stock
Kestrel 3550AG Pocket Delta T Crop Spraying Weather Meter -
Regular price $229.00 USD
Regular price $289.00 USD Sale price $229.00 USD


  • Measurement

    • Wind Speed
    • Current Wind Speed
    • Average Wind Speed
    • Maximum Wind Gust
    • Temperature
    • Barometric Pressure
    • Relative Humidity
    • Wind Chill
    • Heat Stress Index
    • Dew Point Temperature
    • Wet Bulb Temperature (Psychrometric)
    • Temperature-Humidity Index (THI)
    • Altitude (Barometric)
    • Delta-T
    • Wind Direction
    • Bluetooth
  • Includes

    • (1) CR2032 Lithium Battery
    • Instructions
    • Lanyard
    • Certificate Of Conformity (Spec Sheet)
    • Protective Cover - Hard Slip-on
  • Warranty

    5 year manufacturers warranty.
  • Country of origin

    Designed & Built in the USA.

Kestrel 3550AG Bluetooth Weather Meter for Spray Applications

Spray drift can be hazardous to nearby plants and can also cause harm to livestock, people and wildlife.

With the Kestrel 3550AG, you can keep your crop spraying on-target. With it's Bluetooth connectivity, the Kestrel 3550AG will allow you to log data using a smartphone and the Kestrel app with just a simple click.

No matter the size of your operation -- effective herbicide and pesticide application is critical to your success. Prevent drift, eliminate waste, ensure safety and effectiveness – it all starts with monitoring your conditions.

    Field-Level Environmental Monitoring for Reliable Decision-Making

    It is critical to measure relative humidity, wind speed and wind direction at field-level to minimize waste and maximize safety when spraying. The on-site weather at time of application has a significant impact on the risk of drift. Best management practices include checking weather at the site of application to ensure safe and effective spraying. With a built-in digital compass, the 3550AG measures all relevant environmental conditions for spraying including wind direction.

    Experts urge applicators to take measurements at the field location and make decisions from accurate, onsite information. It’s important to measure wind speed at the height of sprayer booms and not rely on readings from the local airport which could be dozens of miles away. The data from remote weather stations do not accurately reflect the conditions at your specific site.

    "If you face any litigation, they will go to nearest airport and get wind speed there," [if no other record exists] "Airfields are typically flat, so the wind speeds are higher there and taken at heights much greater than the boom height of your sprayer. It’s not unusual to find that the wind speed 20 inches above your crop canopy is 2 to 3 mph slower than a nearby airport’s reading."
    -Dr. Bob Beck, Regional Agronomist at Land O'Lakes

    Validation of current conditions meeting label requirements is every applicator’s priority and should be incorporated into all spraying application decisions. With the Kestrel 3550AG, you can easily monitor real-time weather conditions at the field-level.

    Easy Record Keeping for Peace of Mind with the Free Kestrel App

    As regulations surrounding drift management get tighter and media and public attention continues to increase, the stakes are higher than ever for applicators and farmers when it comes to accountability. It’s imperative to document spray conditions to defend against costly litigation and protect the future of your operation. The Kestrel app makes it easy to do by wirelessly connecting to the 3550 so you're able to view, log, and manage weather data on a mobile device. Now you can document field data right at the time of spray application -- forget pen and paper notes that can get lost or attempting to data log hours after the application when you’re back in the office and likely to forget. With just one click, the Snapshot feature in the app captures and saves an instant record of all live measurements along with a GPS-based timestamp. Conveniently export historical data as valuable documented evidence that you sprayed within acceptable weather conditions.

    Pocket sized, rugged, waterproof, affordable, easy-to-use and equipped with on-unit data logging and wireless data retrieval for monitoring and reporting, the Kestrel 3550AG is your trusted weather guide for spraying and farming.

    The new 3550AG meter has Bluetooth connectivity to pair with the Kestrel app for the ability to wirelessly view, share, and export weather data from a mobile device. Download the Kestrel app from the app store to take advantage of the all the features available. 


    • Simple 3-Button Control
    • High Contrast, Sunlight Readable Monochrome LCD Display
    • Backlight (Green)
    • Temperature Sensor (Patented External Isolated)
    • Relative Humidity Sensor
    • CR2032 Coin Cell Battery (Average Life 300 Hours)
    • Data Hold Function
    • Drop-Tested to MIL-STD-810G
    • Waterproof to IP67 (3'/1M for 30 minutes)
    • Kestrel Certificate of Conformity
    • Neck Lanyard
    • Patented Impeller and Sensor Technology
    • Slip-On Protective Cover
    • Time of Day
    • Field Humidity Calibration/Correction Routine
    • User-Replaceable Battery
    • User-Replaceable Impeller
    • Waterproof & Floats
    • Designed and built in the USA

    Physical Dimensions:

    • Dimensions: 4.8 x 1.7 x 0.7 in. / 122 x 42 x 18 mm
    • Weight: 2.3 Ounces / 65 Grams
    • MFG Part# 0835AGLCHVG, Model# 3550AG

      Sensor Specifications

      Wind Speed

      Units of Measure: mph | kt | B | m/s | ft/min / km/h 
      Specification Range:
      • 0.6 to 40.0 m/s
      • 118 to 7,874 ft/min
      • 2.2 to 144.0 km/h
      • 1.3 to 89.5 mph
      • 1.2 to 77.8 knots
      • 0 to 12 B*
      • 2-131.2 F/S*
      Operational Range:
      • 0.6 to 60.0 m/s
      • 118 to 11,811 ft/min
      • 2.2 to 216.0 km/h
      • 1.3 to 134.2 mph
      • 1.2 to 116.6 knots
      • 0 to 12 B*
      • 2-196.9 F/S*
      • 0.1 m/s
      • 1 ft/min
      • 0.1 km/h
      • 0.1 mph
      • 0.1 knots
      • 1 B
      Accuracy (+/-): Larger of 3% of reading, least significant digit or 20 ft/min
      Notes: 1 inch|25 mm diameter impeller with precision axle and low-friction Zytel® bearings. Startup speed stated as lower limit, readings may be taken down to 0.4 m/s | 79 ft/min | 1.5 km/h | .9 mph | .8 kt after impeller startup. Off-axis accuracy -1% @ 5º off-axis; -2% @ 10º; -3% @ 15º. Calibration drift < 1% after 100 hours use at 16 MPH | 7 m/s. Replacement impeller (PN-0801) field installs without tools (US Patent 5,783,753). Wind speed calibration and testing should be done with triangle on impeller located at the top front face of the Kestrel. *F/S only in Ballistics units. Beaufort not available in Ballistics units.

      Ambient Temperature

      Units of Measure: Fahrenheit, Celsius
      Specification Range:
      • -20.0 to 158.0 °F
      • -29.0 to 70.0 °C
      Operational Range:
      • 14.0.0 to 131.0 °F
      • -10.0 to 55.0 °C
      • 0.1 °F
      • 0.1 °C
      Accuracy (+/-):
      • 0.9 °F
      • 0.5 °C
      Notes: Hermetically sealed, precision thermistor mounted externally and thermally isolated (US Patent 5,939,645) for rapid response. Airflow of 2.2 mph|1 m/s or greater provides fastest response and reduction of insolation effect. Calibration drift negligible. Thermistor may also be used to measure temperature of water or snow by submerging thermistor portion into material -- remove impeller prior to taking submerged measurements and ensure humidity sensor membrane is free of liquid water prior to taking humidity-based measurements after submersion.


      Units of Measure: inHg, hPA, mb
      Specification Range:
      • 25°C/ 77°F
      • 750-1100 hPa|mbar
      • 22.15-32.48 inHg
      • 10.88-15.95 PS
      Operational Range:
      • 0.30 to 48.87 inHg
      • 10.0 to 1654.7 hPa|mbar
      • 0.14 to 24.00 PSI
      • 14.0 to 131.0 °F -10.0 to 55.0 °C
      • 0.1 hPa|mbar
      • 0.01 inHg
      • 0.01 PSI
      Accuracy (+/-):
      • 1.5 hPa|mbar
      • 0.044 inHg
      • 0.022 PSI
      Notes: Monolithic silicon piezo-resistive pressure sensor with second-order temperature correction. Between 1100–1600 mbar, unit will operate with reduced accuracy. Sensor may not operate above 1600 mbar and can be damaged above 6,000 mbar or below 10 mbar. Calibration drift is negligible for the life of the product.

      Relative Humidity

      Units of Measure: %
      Specification Range: 5 to 95% 25°C non-condensing
      Operational Range: 0 to 100% 
      Resolution: 0.1 %RH
      Accuracy (+/-): 3%RH
      Notes: To achieve stated accuracy, unit must be permitted to equilibrate to external temperature when exposed to large, rapid temperature changes and be kept out of direct sunlight. Calibration drift is typically less than ±0.25% per year.

      Calculated Measurements

      Wind Chill

      Accuracy (+/-):
      • 1.6 °F
      • 0.9 °C
      • 0.1 °F
      • 0.1 °C
      Sensors employed:
      • Wind Speed
      • Temperature

      Barometric Pressure

      Accuracy (+/-):
      • 0.07 inHg
      • 2.4 hPa|mbar
      • 0.03 PSI
      • 0.01 inHg
      • 0.1 hPa|mbar
      • 0.01 PSI
      Sensors employed:
      • Pressure
      • User Input (Reference Altitude)


      Accuracy (+/-):
      • typical: 23.6 ft/7.2 m
      • from 750 to 1100 mBar
      • max: 48.2 ft/14.7 m
      • from 300 to 750 mBar
      • 1ft
      • 1m
      Sensors employed:
      • Pressure
      • User Input (Reference Pressure)

      Dew Point

      Accuracy (+/-):
      • 3.4 °F
      • 1.9 °C
      • 15-95% RH.
      • Refer to Range
        for Temperature Sensor
      • 0.1 °F
      • 0.1 °C
      Sensors employed:
      • Temperature
      • Relative Humidity

      Wet Bulb Temperature - Psychrometric

      Accuracy (+/-):
      • 3.2 °F
      • 1.8 °C
      • 0.1 °F
      • 0.1 °C
      Sensors employed:
      • Wind Speed
      • Temperature

      Delta T

      Accuracy (+/-):
      • 3.2 °F
      • 1.8 °C
      • 0.1 °F
      • 0.1 °C
      Sensors employed:
      • Temperature
      • Relative Humidity
      • Pressure

      THI (NRC)*

      Accuracy (+/-):
      • 1.5 °F
      • 0.8 °C
      • 0.1 °F
      • 0.1 °C
      Sensors employed:
      • Temperature
      • Relative Humidity
      Notes: * The NRC THI equation is defined as: *THI = (1.8 X Tdb +32) – [(.55 - .0055 X RH) X (1.8 X Tdb-26)] (National Research Council, 1971) where Tdb is dry bulb temperature in °C and RH is relative humidity expressed as a %. This is the equation referenced by Ontario Ministry of Agriculture, Food, and Rural affairs; Journal of Dairy Science; and the University of Arizona. The YOUSEF THI equation is defined as: THI = Tdb + (0.36 × Tdp) + 41.2 (Yousef, 1985) where Tdb is dry bulb temperature in °C and Tdp is dew point temperature in °C. This is the equation referenced by Dairy Australia, University of Missouri, and USDA.

      THI (Yousef)*

      Accuracy (+/-):
      • 2.3 °F
      • 1.3 °C
      • 0.1 °F
      • 0.1 °C
      Sensors employed:
      • Temperature
      • Relative Humidity
      Notes: * The NRC THI equation is defined as: *THI = (1.8 X Tdb +32) – [(.55 - .0055 X RH) X (1.8 X Tdb-26)] (National Research Council, 1971) where Tdb is dry bulb temperature in °C and RH is relative humidity expressed as a %. This is the equation referenced by Ontario Ministry of Agriculture, Food, and Rural affairs; Journal of Dairy Science; and the University of Arizona. The YOUSEF THI equation is defined as: THI = Tdb + (0.36 × Tdp) + 41.2 (Yousef, 1985) where Tdb is dry bulb temperature in °C and Tdp is dew point temperature in °C. This is the equation referenced by Dairy Australia, University of Missouri, and USDA.



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