Our team got hands on with the new DJI Zenmuse L2 payload to put its through its paces and see how it compares with the Zenmuse L1.
Testing location
The testing location was an agricultural property in NSW, Australia. The location was chosen for the creek running through it covered by the dense tree canopy. This allowed our team to put the upgrades of the L2 to the test and see how they affect the ability for it to penetrate vegetation compared to the L1.
Workflow
To ensure accuracy and the ability to compare the L2 to the L1, our team kept universal setting for both payloads where possible, with expectations to the return mode, which went from dual return to penta return on the L2 and the IMU warm up time, which isn't required on the L2.
| Payload | Zenmuse L1 | Zenmuse L2 |
| Scan Mode | Repetitive | Repetitive |
| Return Mode | Dual Return | Penta Return |
| Sample Rate | 240KHz | 240KHz |
| Flight Speed | 6m/s | 6m/s (15m/s used in additional test) |
| Flight Height | 50m | 50m |
| Side Lap | 20% | 20% |
Vegetation penetration
Vegetation penetration with L1 was good, but clarity of tree trunks, layers of the canopy and floor level features was lower when compared to the L2.
It is clear that the precision on the L2 data is higher, with the point cloud having a higher density below the canopy and displaying finer detail, allowing for better and clear quantification of the biomass and topography.
A higher number of returns is also advantageous here, painting a clear picture of the ground level beneath the vegetation.
Vegetation penetration is improved on the L2. The L1 at a ~1m wide strip has clearly visible gaps and holes in the cross-section, while the Zenmuse L2 has a very uniform point density across the entire cross-section.
Both tests visualised were conducted at 50m AGL at 6m/s.
Returns
The L1 with two returns provides some insight to the different levels of vegetation, canopy and ground, while the L2 with five returns provides additional coverage at different levels of the vegetation coverage all the way to ground level.
While in this example there were few returns visible for the fifth echo, it is a feature that industry will be very excited about having the capability to quantify.
Colourisation
The Zenmuse L1 provides reasonable colourisation, however the L2, with better precision is far superior when it comes to colourisation of the point cloud. The smoothness and clarity of the data, including rendering of the surface of the pond, is well defined and an improvement over the L1.
Error data
The data was compared against six ground control points throughout the property and was captured using a Trimble R12 base station.
L1 vs L2 at 50m flying at 6m/s
L1 Check Point Error
| Parameters | Average Altitude Difference | Min Altitude Difference | Max Altitude Difference | Average Absolute Value of Altitude Difference | Root Mean Square | Standard Deviation |
|---|---|---|---|---|---|---|
| -0.091692 | -0.186136 | 0.013588 | 0.096221 | 0.109237 | 0.119663 |
L1 Error info
| ID | X/E | Y/N | Z/U | Reconstruction Altitude | Altitude Difference | Reflectivity |
|---|---|---|---|---|---|---|
| Drtk2 | 290004.673 | 6239640.204 | 75.354 | 75.367588 | 0.013588 | 68.090909 |
| 1-ldg | 290001.675 | 6239627.636 | 75.574 | 75.451981 | -0.122019 | 64.457557 |
| 2-fence | 290009.237 | 6239559.802 | 75.682 | 75.495864 | -0.186136 | 92.017341 |
| 3-fence-sw | 289895.248 | 6239532.422 | 76.705 | 76.626797 | -0.078203 | 74.581921 |
| 4-dam | 289875.98 | 6239615.336 | 79.261 | 79.168546 | -0.092454 | 108.083333 |
| 5-north-mid | 289939.444 | 6239622.926 | 75.923 | 75.838072 | -0.084928 | 69.177285 |
The DJI Terra processed data showed an RMS Z-accuracy of 10.9cm which with post processing and a PPK workflow could likely be further improved.
L2 Check Point Error
| Parameters | Average Altitude Difference | Min Altitude Difference | Max Altitude Difference | Average Absolute Value of Altitude Difference | Root Mean Square | Standard Deviation |
|---|---|---|---|---|---|---|
| -0.044028 | -0.142643 | 0.059995 | 0.064026 | 0.073567 | 0.080588 |
L2 Error info
| ID | X/E | Y/N | Z/U | Reconstruction Altitude | Altitude Difference | Reflectivity |
|---|---|---|---|---|---|---|
| Drtk2 | 290004.673 | 6239640.204 | 75.354 | 75.413995 | 0.059995 | 78.695266 |
| 1-ldg | 290001.675 | 6239627.636 | 75.574 | 75.515366 | -0.058634 | 77.292553 |
| 2-fence | 290009.237 | 6239559.802 | 75.682 | 75.539357 | -0.142643 | 81.434434 |
| 3-fence-sw | 289895.248 | 6239532.422 | 76.705 | 76.662958 | -0.042042 | 64.670588 |
| 4-dam | 289875.98 | 6239615.336 | 79.261 | 79.215438 | -0.045562 | 77.672222 |
| 5-north-mid | 289939.444 | 6239622.926 | 75.923 | 75.887718 | -0.035282 | 80.442308 |
The DJI Terra processed data showed an RMS Z-accuracy of 7.3cm which is an improvement over the L1.
L2 at 50m flying at 15m/s
Check Point Error
| Parameters | Average Altitude Difference | Min Altitude Difference | Max Altitude Difference | Average Absolute Value of Altitude Difference | Root Mean Square | Standard Deviation |
|---|---|---|---|---|---|---|
| -0.037739 | -0.124399 | 0.062959 | 0.058726 | 0.066973 | 0.073366 |
Error info
| ID | X/E | Y/N | Z/U | Reconstruction Altitude | Altitude Difference | Reflectivity |
|---|---|---|---|---|---|---|
| Drtk2 | 290004.673 | 6239640.204 | 75.354 | 75.416959 | 0.062959 | 80 |
| 1-ldg | 290001.675 | 6239627.636 | 75.574 | 75.522421 | -0.051579 | 77.92029 |
| 2-fence | 290009.237 | 6239559.802 | 75.682 | 75.557601 | -0.124399 | 76.960396 |
| 3-fence-sw | 289895.248 | 6239532.422 | 76.705 | 76.676678 | -0.028322 | 66.75 |
| 4-dam | 289875.98 | 6239615.336 | 79.261 | 79.204479 | -0.056521 | 78.25641 |
| 5-north-mid | 289939.444 | 6239622.926 | 75.923 | 75.894426 | -0.028574 | 79.494382 |
The L2 was able to be flown at up to 15m/s, improving the efficiency of the capture, while still maintaining 6-7cm RMS accuracy as achieved at 6m/s. PPK or processing using Terrascan may be able to further refine the data.
All data from DJI Terra v3.9.0
Benefits of the DJI Zenmuse L2
The L2 introduces a number of improvements over the L1 including being more accurate and precise with an RMS z-accuracy of 7.3cm compared to 10.9cm. The L2 also has improved vegetation penetration with the generated point clouds having a higher density below the canopy as well as showing finer details.
L2 can fly at 15m/s making data capture faster when compared with the L1, while still ensuring data quality. Zenmuse L2 can achieve an RMS z-accuracy of 6-7cm at 15m/s, in line with quality when flying at 6m/s with the L2.
Zenmuse L2 no longer requires an IMU warmup period allowing for quicker deployment and turnround between flights. L1 requires 5-10 minutes for the IMU to warmup.
Thanks to the combination of higher precision and an improved RGB camera, the L2 produces a more accurate colour rendition of scenes.
