DJI Mavic 3 Multispectral
The DJI Mavic 3 Multispectral (Mavic 3M) is an extremely portable, highly sophisticated platform with built-in high quality 20Mp photogrammetry and 4-band multispectral sensors, supported by cm-level RTK positioning.
The Mavic 3M provides an extremely portable system with very intuitive interfaces. Mission planning takes a matter of moments, even in complex terrain.
All bands lie within the Visible-Near Infrared range.
For full specifications see the DJI website: DJI Mavic 3M - Specifications - DJI
|Max Take-Off Weight
|951g with RTK module; max 1050g
|Max Payload Weight
|N/A - sensor is fully integrated
|2.4000-2.4835 GHz 5.725-5.850 GHz
Service Ceiling Above Sea Level
cm-level precision with RTK system enabled
Max Wind Resistance
|-10°C to 40°C
Max Flight Time
In practice ~ 25 min useful flight time with safe reserves
The Mavic 3M features a fully integrated sensor which combines a 20Mp photogrammetry camera with a 4-band multispectral sensor. The multispectral sensor is supported by an irradiance light sensor built into the top of the aircraft. Full specifications of the sensor package are available at the DJI website here: DJI Mavic 3M - Specifications - DJI
The Mavic 3M uses real-time RTK GNSS corrections to tag its data with cm-level precision. There are various options for providing the real-time RTK GNSS corrections and translating high relative positioning accuracy to high absolute accuracy.
Using the D-RTK-2 Mobile Station
Our D-RTK-2 mobile station is specifically designed to support DJI's RTK-equipped aircraft such as the M300 RTK and Mavic 3M by providing real-time corrections to the aircraft which yield cm-level relative positioning accuracy between the mobile station and the aircraft. This system is entirely stand-alone and does not require any external network or mobile connectivity, so it is suitable for use in all environments, even where strong stable 4G mobile connectivity cannot be assured.
While this relative positioning accuracy will be enough for many applications, it is important to note that the mobile station does not, by default, know it's own position in absolute terms to the same level of accuracy. To achieve cm-level absolute positioning accuracy additional steps are therefore required. There are various options as outlined below:
- If the absolute position of the D-RTK-2 mobile station is already known to cm-level accuracy by pre-survey, this data can be input directly into the D-RTK-2 during set-up in the field. The corrections are then incorporated in the real-time data transmitted to the aircraft and logged in the acquired data.
- If the absolute position of the D-RTK-2 mobile station is not known in advance, but surveyed on the same day as the flight acquisition, the accurate position of the station can be entered into the DJI Terra software during initial post-processing of the acquired data, which will then update the positional information throughout the dataset.
- We are looking into workflows to process the recorded D-RTK-2 data against external base station networks (e.g. Ordnance Survey) in post-processing, to produce an accurate reference against which to correct the acquired flight data. This would remove the need to independently survey the D-RTK-2 location. Note that this is a work in progress and not yet in place.
Using Network RTK
If a stable 4G mobile connection can be assured, it is possible for the Mavic 3M to use a mobile connection to receive real-time corrections from commercial networks of RTK base stations, which negates the need for the D-RTK-2 mobile station and reduces the amount of field equipment required.
This workflow requires both a strong and stable 4G mobile network connection at the operating site and also access to a commercial RTK network with nearby base stations, which may not be available in some parts of the world. Access to such networks incurs cost, typically of around £25 / day for access to the RTK base station network, and of course any charges for mobile network access (e.g. via hotspot or dongle).
Note that while such base stations should know their own positions to high accuracy, we believe that there will be a dilution of positional accuracy with increasing distance between the selected network base station and the aircraft of around 1ppm. At time of writing we are yet to test and evaluate this workflow; due to the remote nature of the majority of our work, 4G connections cannot usually be assured and the D-RTK-2 workflow above is our default mode of operation.
Use of Ground Control and Check Points
The Mavic 3M's RTK positioning system provides very accurate data tagging as outlined above. In many cases this may be considered to negate the need for any ground control points. However, for those applications where absolute positioning and / or scale accuracy are critical, it remains good practice to also incorporate independently surveyed ground control points (to further constrain the generated models) and / or check points (to provide an accuracy assessment of the final product). Typically 8-10 ground control points and 4-6 check points should be distributed around the survey area. If it is not possible to access the survey area for ground control point distribution and survey, then check points around the take-off and landing site may still provide a useful degree of accuracy assessment.
We operate an Emlid Reach RS GNSS survey system for the survey of ground control points, check points and the location of the D-RTK-2 mobile station. This is included as an optional add-on to the Mavic 3M carrying system as outlined below. For eligible projects more modern and compact survey systems are also available through the NERC Geophysical Equipment Facility (GEF).
The Mavic 3M is an extremely portable system. The aircraft itself, along with controller and 6 flight batteries, fits into a small hard carrying case. Along with supporting equipment (landing pad, safety equipment, calibration panel, additional batteries etc.) it fits easily into a single 75L pack.
If the D-RTK2 base unit is required, this involves another backpack and tripod, and the Emlid ground survey GNSS system and ground control points, if needed, will require a third pack, an additional tripod and rover pole.