Erratum: Du, K., et al. Simulation of Ku-Band Profile Radar Waveform by Extending Radiosity Applicable to Porous Individual Objects (RAPID2) Model. Remote Sensing 2020, 12, 684

The authors wish to make the following corrections to this paper [1]:

1. Change in Author Names (Add Four New Authors)

In the original version of our paper [1], insufficient acknowledgement was given for the source of Tomoradar and lidar data used. We apologize for the original error. To correct this oversight, we wish to add Ziyi Feng, Teemu Hakala, Yuwei Chen and Juha Hyyppä as authors of our paper [1]. The updated list of the authors of this paper and their affiliations are provided below:

Kai Du ¹, Huaguo Huang ^1,*, Yuyi Zhu ², Ziyi Feng ³, Teemu Hakala ³, Yuwei Chen ³ and Juha Hyyppä ³

• ¹ The Key Laboratory for Silviculture and Conservation of Ministry of Education, Beijing Forestry University, Beijing 100083, China; [email protected]
• ² Sichuan Forestry and Grassland Inventory and Planning Institute, Chengdu 610081, China; [email protected]
• ³ Department of Photogrammetry and Remote Sensing, Finnish Geospatial Research Institute, National Land of Survey, FI-02431 Kirkkonummi, Finland; [email protected] (Z.F.); [email protected] (T.H.); [email protected] (Y.C.); [email protected] (J.H.)

* Correspondence: [email protected]; Tel.: +86-10-6233-8133

2. Change in Author Contributions

The updated “Author Contributions” is provided below:

• Author Contributions: K.D. and H.H. modified the program of the RAPID2 model; Y.Z. estimated the tree LAIs with lidar data; Z.F. and T.H. completed the pre-processing of the Tomoradar and lidar data; Y.C. and J.H. instructed data collection and analysis, reviewed the paper; K.D. analyzed the data; K.D. wrote the paper; H.H. reviewed the paper. All authors have read and agreed to the published version of the manuscript.

3. Change in Main Body Paragraphs

The authors are sorry to report that there are seven mistakes in this paper [1]. On page 7, lines 28, the location of Evo “61°19′N, 25°11′S” should be “61°19′N, 25°11′E”. On page 8, lines 11, the sentence “Tomoradar can receive waveform of four polarization modes (HH, HV, VH, and VV) with 0.14-m range resolution.” should be “Tomoradar can receive waveform of four polarization modes (HH, HV, VH, and VV) with 0.15-m range resolution.”. On page 8, Table 2, due to the mistake of range resolution (0.14 m),

Table 2. Main parameters of Tomoradar. FM-CW: Frequency Modulated Continuous Wave.

Parameters	Specified Values
Center frequency (GHz)	14
Range resolution (m)	0.14
Field of view (°)	6
Polarization modes	HH, HV, VH, VV
Modulation type	FM-CW
Modulation frequency (Hz)	163
Data rate (Mbits/s)	2.5

Table 2. Main parameters of Tomoradar. FM-CW: Frequency Modulated Continuous Wave.

Parameters	Specified Values
Center frequency (GHz)	14
Range resolution (m)	0.14
Field of view (°)	6
Polarization modes	HH, HV, VH, VV
Modulation type	FM-CW
Modulation frequency (Hz)	163
Data rate (Mbits/s)	2.5

should be updated as:

Table 2. Main parameters of Tomoradar. FM-CW: Frequency Modulated Continuous Wave.

Parameters	Specified Values
Center frequency (GHz)	14
Range resolution (m)	0.15
Field of view (°)	6
Polarization modes	HH, HV, VH, VV
Modulation type	FM-CW
Modulation frequency (Hz)	163
Data rate (Mbits/s)	2.5

Table 2. Main parameters of Tomoradar. FM-CW: Frequency Modulated Continuous Wave.

Parameters	Specified Values
Center frequency (GHz)	14
Range resolution (m)	0.15
Field of view (°)	6
Polarization modes	HH, HV, VH, VV
Modulation type	FM-CW
Modulation frequency (Hz)	163
Data rate (Mbits/s)	2.5

On page 12, lines 1–2, the sentence “To ensure the effectiveness of the comparison, the range resolution of the simulated waveforms has been set to 0.14 m with a footprint-width of 6 m, matching with measured data parameters.” should be “To ensure the effectiveness of the comparison, the range resolution of the simulated waveforms has been set to 0.15 m with a footprint-width of 6 m, matching with measured data parameters.”. On page 14, lines 15–17, the sentence “Since the vertical resolution of the simulated waveforms was set to 0.14 m, which is consistent with Tomoradar data, the error of penetration depth calculation was not less than 0.14 m.” should be “Since the vertical resolution of the simulated waveforms was set to 0.15 m, which is consistent with Tomoradar data, the error of penetration depth calculation was not less than 0.15 m.”. On page 16, lines 25, the sentence “The vertical resolution of waveform simulated in this paper is 0.14 m.” should be “The vertical resolution of waveform simulated in this paper is 0.15 m.” On page 16, lines 28–30, the sentence “Second, the quality of Tomoradar is higher, for example, the vertical resolution is 0.14 m, which means the simulation in our study can more accurately characterize the backscattering profiles of true forest, but it is possible to make more errors in details as well.” should be “Second, the quality of Tomoradar data is higher, for example, the vertical resolution is 0.15 m, which means the simulation in our study can more accurately characterize the backscattering profiles of true forest, but it is possible to make more errors in details as well.”.

Recently, through discussions with the newly added authors, we wish to revise two parts of the comparison of simulation results section and discussion section. On page 12, lines 13–15, the sentence “Therefore, errors appeared in simulations, especially at cross-polarization. Small sub-layers were not simulated in canopy (Figure 9d).” should be modified to “In addition, the Tomoradar data showed hairy and jagged due to background noise, which did not exist in the simulated data. Therefore, the difference appeared between the simulated data and Tomoradar data, especially at cross-polarization.” On page 16, line 39–41, the sentence “In this study, we had to fix them, for a crown, without varying from top to bottom, because we did not have the corresponding ground measurement.” should be modified to “Another possible explanation is that the cross-polarization signals suffer from a higher proportion contribution of background noise, because the backscattering intensity of cross-polarization signals is significantly weaker than that of co-polarization. Noise floor of the FM-CW radar is typically determined by the internal reflections. In this study, we had to fix the density of twig, for a crown, without varying from top to bottom, because we did not have the corresponding ground measurement, in addition, background noise caused by internal reflections did not exist in simulations.”

4. Change in Acknowledgement

Due to a lapse, the Acknowledgement section was missing in the original article version [1]. The authors wish to add the section for sufficient acknowledgments:

• Acknowledgments: Chinese Academy of Science (181811KYSB20160040), Shanghai Science and Technology Foundations (18590712600) and Beijing Municipal Science and Technology Commission (Z181100001018036), Jihua Lab (X190211TE190) are acknowledged. Additionally, the author also gratefully acknowledges the financial support from Academy of Finland projects “Estimating Forest Resources and Quality-related Attributes Using Automated Methods and Technologies” (Academy decision 334830).

These changes have no material impact on the conclusions of our paper. The authors would like to apologize for any inconvenience caused to the readers by these changes.