Parameterization of Urban Sensible Heat Flux from Remotely Sensed Surface Temperature: Effects of Surface Structure
and Xiaoying Ouyang 3
Round 1
Reviewer 1 Report
The paper is quite novel and has applications in micro-scale modeling of urban fluxes using thermal infrared remote sensing. The authors clearly had future users in mind when designing the study and writing the paper, which I greatly appreciate. I enjoyed reading the paper.
Some general comments:
- In generally, you should remove "the" when it is in front of a common noun. e.g. Line 49, "The urban morphology significantly..." should read "Urban morphology significantly...".
- Figures need to be improved. I would suggest resampling them at a higher DPI or as a vector file. They are quite difficult to read, particularly on high-res screens.
- I would have a table that resistances, and temperatures defined in it. I had to flip back and forth through the manuscript to remember what each of the resistance terms represented
- You indicate at the end that the parameterization is only representative for subtropical areas. I have two questions from this: (1) How do you recommend the reader re-calculate coefficients? By using high-res thermal imagery and TUF-3D in a new setting? If so, how transferable is this method? I think being a little more clear about how the reader should go about using the parameterization in different climates would improve usability. (2) You state that that TUF-3D was used to model sensible fluxes for a desert city and that there was good agreement. If fluxes are sensitive to background climate, is the desert study applicable here in terms of stating that TUF-3D is suitable for this study? Are there any studies that have used TUF-3D to model fluxes in more representative climates?
- I would like to know the magnitude of the difference between nadir Tsurf (or radiometric Tsurf in the paper) and complete Tsurf. A diurnal plot of this would be helpful for the four dates.
Specific comments:
Line 38 - 40. I think this sentence is backwards. Turbulent exchange is a major component of heat and mass exchange in the BL and sensible heat is a major component of turbulent exchange.
Lines 46 – 56. This paragraph repeats itself several times. I think you can make it much shorter.
Line 59. Missing a space in “[17-26].The”.
Line 63. Change “blocking (radiative shading)” to “shading”. What is the “real” surface temperature? Based on the rest of this sentence, it is not the complete surface temperature. This needs to be more clear.
Line 80. Change to “…should be corrected by improving the resistance estimation”
Line 131 – 132. Should read, “Facet temperature is calculated based…”
Line 157 – 158: I am confused as to why you talk about atmospheric correction of top of atmosphere radiance. Do you mean in order to calculate Ldown?
Line 204 – 207. This is the first time the reader is told what the paper is going to do. I would make this clearer much earlier in the paper.
Line 237 – 239. Need to know more parameters about the camera. You provide the reference, but it would be nice to know make, model FOV, swath width, how the camera was flown, etc.
Evaluation: It would be nice to know some more specifics about the study area. Could you show a true color image? How was the area represented in TUF-3D? Could you show the geometric mock-up you used in TUF?
Line 265. Missing a space in “…roughness can decrease[35]…”
Line 287 – 289. This sentence is unclear, I recommend splitting into two sentences.
Line 380. I was a little confused where the reader should estimate H/Rn from? Literature? Is that integrated over a day or maximum? Should be more clear.
Figure 6. The residuals of this plot do not look normal. Is a polynomial fit for the parameterization the most valid option? Did you test other fits? The parameterization is quite useful, but it is clear to me that the fit is poor.
Figure 7: The axis limits of this plot are too large. The largest values on the x and y should be 1000 W/m2. Are these values from the four validation dates?
Line 459: You mention bias. In what direction? Be more specific.
Line 462 – 480. Many spelling mistakes in this paragraph, please proofread.
Author Response
Comments and Suggestions for Authors
The paper is quite novel and has applications in micro-scale modeling of urban fluxes using thermal infrared remote sensing. The authors clearly had future users in mind when designing the study and writing the paper, which I greatly appreciate. I enjoyed reading the paper.
Reply: we appreciate the reviewer’s hard work for our draft and thanks for your valuable comments to improve our draft.
Some general comments:
- In generally, you should remove "the" when it is in front of a common noun. e.g. Line 49, "The urban morphology significantly..." should read "Urban morphology significantly...".
Reply: Thanks! We have checked the draft, and deleted “the” in front of common nouns.
- Figures need to be improved. I would suggest resampling them at a higher DPI or as a vector file. They are quite difficult to read, particularly on high-res screens.
Reply: Thanks! Figures have been improved to higher resolution.
- I would have a table that resistances, and temperatures defined in it. I had to flip back and forth through the manuscript to remember what each of the resistance terms represented
Reply: Thanks! A table with the summary of definitions and symbols used in this study has been added in the Section 2.4 Methodology.
- You indicate at the end that the parameterization is only representative for subtropical areas. I have two questions from this: (1) How do you recommend the reader re-calculate coefficients? By using high-res thermal imagery and TUF-3D in a new setting? If so, how transferable is this method? I think being a little more clear about how the reader should go about using the parameterization in different climates would improve usability.
Reply: In this study, the meteorological data is from Hong Kong Observatory. We used both summer and winter data. The value range of meteorological data can cover most conditions of mid-altitude and subtropical local climate. So we think the coefficients in this study can be transferred to a wider range of climate conditions. For the area with extreme cold climates in the high-altitude areas, more studies will be conducted in the near future if possible. The sentences that state that this parameterization is only representative for subtropical areas have been deleted.
(2) You state that that TUF-3D was used to model sensible fluxes for a desert city and that there was good agreement. If fluxes are sensitive to background climate, is the desert study applicable here in terms of stating that TUF-3D is suitable for this study? Are there any studies that have used TUF-3D to model fluxes in more representative climates?
Reply: Thanks for pointing this out. Our wording of this paragraph might have been slightly misleading. First, Andacollo is not really characterized by a desert climate: the mean annual temperature is 12.1 °C and the mean annual rainfall is 97 mm, i.e. rather different from Hong Kong, where our weather data were collected. In addition we focused our comments on the evaluation of the accuracy of TUF 3D against in-situ measurements. The model has been evaluated in multiple environments, see e.g. Krayenhoff and Voogt (2007), which support the applicability of TUF 3D to diverse climate conditions.
Accordingly we have re-arranged and rephrased this paragraph (L148 – 157) as follows:
“TUF-3D has also been used to simulate the sensible heat fluxes in a lightweight low-rise neighborhood at Andacollo, Chile and results were compared with observations and a local-scale empirical model (LUMPS) for a 14-day period in autumn 2009. The results showed good agreement between observed and modelled sensible heat fluxes [39]. TUF-3D was originally tested against urban climate, surface temperature and energy balance data from Vancouver, Canada and Basel, Switzerland, and it has been applied in diverse cities. These prior model evaluations support the application of TUF-3D to model the urban sensible heat flux, the complete and the radiometric surface temperatures for different urban geometries, seasons and climates. More details about facet surface temperature and sensible heat flux simulation in TUF-3D can be found in [39].
- I would like to know the magnitude of the difference between nadir Tsurf (or radiometric Tsurf in the paper) and complete Tsurf. A diurnal plot of this would be helpful for the four dates.
Reply: Thanks for your suggestion! The magnitude of the difference between Tc and Tr depends on the geometry and climate conditions. We added in the appendix a diurnal plot of Tc and Tr for the four dates when is 0.25 and H/L is 1.0. In this condition and around noon, the difference between Tc and Tr can reach 8 in the summer and 5 in the winter. When and H/L increase, the difference between Tc and Tr will increase. This information has been added in Line 211 to 214.
Specific comments:
Line 38 - 40. I think this sentence is backwards. Turbulent exchange is a major component of heat and mass exchange in the BL and sensible heat is a major component of turbulent exchange.
Reply: Thanks for your suggestion! This sentence has been revised as “Turbulent heat exchange in urban areas is a major component of heat and mass transfer from the urban canopy to the atmospheric boundary layer and sensible heat flux is a major component of turbulent exchange.”
Lines 46 – 56. This paragraph repeats itself several times. I think you can make it much shorter.
Reply: thanks for your suggestion! This paragraph has been revised and the repeated parts have been deleted.
Line 59. Missing a space in “[17-26].The”.
Reply: It has been revised as suggested.
Line 63. Change “blocking (radiative shading)” to “shading”.
Reply: the sentence has been revised as suggested.
What is the “real” surface temperature? Based on the rest of this sentence, it is not the complete surface temperature. This needs to be more clear.
Reply: Here the real surface temperature is the complete surface temperature. This sentence has been revised.
Line 80. Change to “…should be corrected by improving the resistance estimation”
Reply: This sentence has been revised as suggested.
Line 131 – 132. Should read, “Facet temperature is calculated based…”
Reply: This sentence has been revised as suggested.
Line 157 – 158: I am confused as to why you talk about atmospheric correction of top of atmosphere radiance. Do you mean in order to calculate Ldown?
Reply: sorry for the confusion. This sentence has been deleted.
Line 204 – 207. This is the first time the reader is told what the paper is going to do. I would make this clearer much earlier in the paper.
Reply: Thank you for this suggestion. The following sentence has been inserted at the end of the Introduction (L129 – 132)
“The objective of this study is to derive an effective resistance for calculation of urban sensible heat flux from radiometric (nadir view) surface temperature. Pseudo-observations generated by numerical experiments with the TUF – 3D model were used for this purpose.”
Line 237 – 239. Need to know more parameters about the camera. You provide the reference, but it would be nice to know make, model FOV, swath width, how the camera was flown, etc.
Evaluation: It would be nice to know some more specifics about the study area. Could you show a true color image? How was the area represented in TUF-3D? Could you show the geometric mock-up you used in TUF?
Reply: the FOV of the camera is 24 , the flight height was about 500 m. this information has been added in the draft (Line 265 to 267). The true color image about the research area has been added in the draft. The research area has little vegetation. The geometric parameters ( and F) were calculated by the GIS building data.
Line 265. Missing a space in “…roughness can decrease[35]…”
Reply: Thanks! it has been revised.
Line 287 – 289. This sentence is unclear, I recommend splitting into two sentences.
Reply: Thanks for your comment. The sentence has been rewritten as:
“The area of wall facets per unit horizontal area increases with increasing lp. This increases the fraction of urban area that is not captured by a nadir-looking radiometer, thus increasing the difference between and , leading to a higher at higher .“
Line 380. I was a little confused where the reader should estimate H/Rn from? Literature? Is that integrated over a day or maximum? Should be more clear.
Reply: Thanks for your comment. Our point of view is that the ratio H/Rn has limited impact on the performance of the parameterization, except the extreme case H/Rn < 0.1, which would be expected at high latent heat flux, i.e. in an urban neighborhood with a large fraction of vegetation. Also it does not need to be estimated very accurately, i.e. estimates based on literature or initial numeric experiments or measurements (if available) would be sufficient to estimate whether H/Rn would be significantly higher than 0.1.
To clarify this aspect we have modified the manuscript in different ways:
1) We have added a comment on Table 2 at L 419 to 421:
“In other words, in most cases, it is not really necessary to estimate H/Rn to determine the appropriate values of the coefficients in Eq.7. Additional comments on this aspect can be sound in Sect.4 Discussion.”
2) We have also edited L411-412 as:
“When the ratio of daytime total sensible heat flux to daytime total net radiation (H/Rn) is higher than 0.1,”
3) We have adapted the comments in Sect. 4 Discussion (L493 – 497) on the impact of H/Rn on the parameterization to read:
“In our view, the impact of H/Rn on the accuracy of estimated rr is significant only when H/Rn < 0.1. This case is likely to apply when latent heat flux is large, i.e. to urban neighborhoods characterized by a large fraction of vegetation. Under these conditions an additional resistance would still be needed to estimate H from Tr, but such resitance would depend on vegetation rather than urban geometry. “
Figure 6. The residuals of this plot do not look normal. Is a polynomial fit for the parameterization the most valid option? Did you test other fits? The parameterization is quite useful, but it is clear to me that the fit is poor.
Reply: Thanks for the comment. We have added the following clarification at L405 to 409.
“The form of the parametrization (Eq..7) is based on the analysis of the dependence of the additional resistance on geometric parameters. The dependence of rr on F is logarithmic (Fig.5), while it is nearly linear on lp (Fig. 4). Similar evaluations (not shown) for the remaining parameters in Eq.7 did suggest a linear relationship. This led to choose the polynomial form of Eq.7.”
In any case, in our view, the accuracy of estimated H (see Fig.7) is satisfactory.
Figure 7: The axis limits of this plot are too large. The largest values on the x and y should be 1000 W/m2. Are these values from the four validation dates?
Reply: thanks for your suggestion! The axis limits have been revised as suggested. The values are from the high resolution thermal data observed on August 6 2013.
Line 459: You mention bias. In what direction? Be more specific.
Reply: Thanks for your comment. We apologize for the confusion. We have evaluated the performance of the proposed method by applying the RMSE metric. Accordingly, we have replaced “bias” with “RMSE” wherever applicable.
Line 462 – 480. Many spelling mistakes in this paragraph, please proofread.
Reply: Thanks for your suggestion! The grammar and spelling mistakes have been revised.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper is well-structured and well-prepared. Although the novelty is limited considering the literature and publications of the authors, it has important findings. I recommend that all authors read the paper one more time for checking punctuation and spelling. If the editorial office corrects them then it can be published as it is.
Author Response
The paper is well-structured and well-prepared. Although the novelty is limited considering the literature and publications of the authors, it has important findings. I recommend that all authors read the paper one more time for checking punctuation and spelling. If the editorial office corrects them then it can be published as it is.
Reply: Thanks for comments for our draft. We have checked and revised the grammar and spelling.
Reviewer 3 Report
The study aim is to present the Parameterization of urban sensible heat flux from remotely-sensed surface temperature: effects of surface structure. The manuscript is presented in a clear and nice way. I would like to suggest minor revision for this paper.
comments:
1. Need to add citations for line 46-56
2. You have to explain the limitation of the study.
Author Response
comments:
1. Need to add citations for line 46-56
Reply: Thanks for your suggestions! More citations have been added in that paragraph.
2. You have to explain the limitation of the study.
Reply: the contents from Line 489 to 516 are about the limitation of this study. We added the sentence “There are several limitations to this study” to clarify where this issue is dealt with.
Round 2
Reviewer 1 Report
The authors have addressed all of my comments.
