Feasibility for Operationally Monitoring Ground-Based Multichannel Microwave Radiometer by Using Solar Observations
, Zhenhui Wang 1,2, Jiang Qin 3,4, Lei Zhu 3,4, Rui Chen 3,4, Jianping Lu 3,4 and Yingying Ma 5,*Round 1
Reviewer 1 Report
This manuscript describes a method of monitoring the operation of a ground-based microwave radiometer, by scanning the sun. Other operators of such atmospheric-measurement instruments may find it useful.
The manuscript would benefit from editing by someone proficient in English. Hopefully the journal can provide that. A few examples:
lines 19 and 49:"they are lack of unified monitor" -> they lack a unified monitor...
line 105: I don't understand what is meant by a "schematic antenna system".
line 183: The English term is great circle, not "large circle".
Other comments:
lines 130-133: Acronyms PPI and RHI should be defined.
Eq.3 applies when the antenna is pointed directly at the sun, not "when the antenna scans the sun".
In eq.5, d is not defined.
Figures 4 and 5 apparently show fitting of a Gaussian model after the sun has been located exactly, as explained in section 4.2. The presentation would be clearer if the material in sections 4.2 and 4.1 were reversed in order.
In figure 9, please clarify whether each dot corresponds to a separate run?
Author Response
Dear Editors and Reviewers:
Thank you very much for your letter and for the reviewers’ comments concerning our manuscript. The comments are all valuable and very helpful for revising and improving our paper. We have studied comments carefully, and have made corrections and modification which we hope meet with approval. We have been trying our best to improve the manuscript. Please check the revised version of the manuscript.
Point 1: lines 19 and 49:"they are lack of unified monitor" -> they lack a unified monitor...
Response 1: We have corrected this part according to the suggestions.
Point 2: line 105: I don't understand what is meant by a "schematic antenna system".
Response 2: It was my mistake and we have corrected this part according to the suggestions.
Point 3: line 183: The English term is great circle, not "large circle".
Response 3: We have corrected according to the suggestion.
Point 4: lines 130-133: Acronyms PPI and RHI should be defined.
Response 4: PPI: Polar Plane Indicator. RHI: Range Height Indicator. We have corrected this part according to the suggestions.
Point 5: Eq.3 applies when the antenna is pointed directly at the sun, not "when the antenna scans the sun".
Response 5: We have corrected this part according to the suggestions.
Point 6: In eq.5, d is not defined.
Response 6: It was my mistake and we have corrected according to the suggestion.
Point 7: Figures 4 and 5 apparently show fitting of a Gaussian model after the sun has been located exactly, as explained in section 4.2. The presentation would be clearer if the material in sections 4.2 and 4.1 were reversed in order.
Response 7: We have corrected this part according to the suggestions.
Point 8: In figure 9, please clarify whether each dot corresponds to a separate run?
Response 8: The interval between data points is fixed (1°) on the horizontal axis. We have corrected this part according to the suggestions. Please check the section 4.4.2.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Synopsis
This paper presents a method to determine the antenna patterns for the GMRs from solar scans, and compares the antenna patterns with those derived from the anechoic chamber. The authors suggest that this method can produce consistent results as from the anechoic chamber and can be used for routine monitoring of GMRs. Major concern of this study is that the sun has been used as target for antenna pattern studies before. So, the current study is lack of novelty.
General Comments:
Some technical details of this method/application are missing.
- What are the sources of the uncertainty?
- How did the authors take into account the movement of the sun’s position during one scan?
- Did the authors perform several scans under different conditions and/or solar elevation angles for morning/noon/night? (e.g. summer/winter, morning/noon)?
- How did the authors get the “daily mean” beamwidth, gain, and aperture efficiency as shown in Figs. 7 and 8?
- The authors recommend this method being applied routinely. However, it requires clear-sky conditions. Just like shown in Figs. 7 and 8, there are not many days satisfied clear-sky condition in 15 months. Therefore, how to compensate for such rigid conditions in order to apply this method routinely?
- The meaning of section 4.4 “The effect of atmospheric refraction” is unclear.
- Figures are not ordered sequentially.
Detail Comments
- Line 47: missing “the” in front of “last few”
- Line 50: “generally” should be “general”
- Line 54, 55: “modelled” should be “modeled”
- Line 130: please spell out “PPI”
- Line 133: please spell out “RHI”
- Line 166: “to use” should be “using”
- Line 174: “an elevation” should be “and elevation”
- Line 186: how much will the “angle distortion” affect the method?
- Line 192: please explain “other effects”, and how much will they affect the uncertainty
- Line 199. “However, it can be calculated by observing the sun”. Could the authors add more explanation and references?
- Line 223 and 232: “least squares” should be “least-square”
- Line 241: missing “on” in front of “the point”
- 3, 4, and 5: what is the time stamp for this experiment?
- Line 262: missing “a” in front of “small bias”
- Line 268: “a slightly offset is still seen in the center”. Could the authors quantify the value of the offset? “slightly” should be “slight”
- Line 272: redundant “of” in front of “between”
- 7 and 8: How many days are included in these two figures?
- Line 313 and 319: “in field” should be “in-field”
- Line 329: redundant “the” in front of “Figure 9”
- Line 330: missing “the” in front of “radiative”
- Line 339: “an extension of the method”. Could the authors justify this statement?
- Line 352-353, “In the daily average system…” Please rephrase this sentence.
- Line 359: “independent” should be “independently”
Author Response
Dear Editors and Reviewers:
Thank you very much for your letter and for the reviewers’ comments concerning our manuscript. The comments are all valuable and very helpful for revising and improving our paper. We have studied comments carefully, and have made corrections and modification which we hope meet with approval. We have been trying our best to improve the manuscript. Please check the revised version of the manuscript.
General Comments:
Point 1: What are the sources of the uncertainty?
Response 1: The sources of the uncertainty include the systematic errors, antenna pointing error, the effect of atmospheric refraction and the antenna beamwidth. These errors can be calibrated. In addition, the effect of antenna efficiency, a misalignment between the horn and the parabolic reflector, the non-uniform distribution of the solar TB can also introduce errors, but these errors can be ignored.
And the description above has been added to the manuscript. Please check the section 4.4.
Point 2: How did the authors take into account the movement of the sun’s position during one scan?
Response 2: The azimuth and elevation step angle Δθa and Δθe are the relative position between the antenna beam pointing and the sun. Since the sun is moving along the sky within scanning time interval, we adjusted to control the antenna pointing to scan the sun, and we need to re-calculate the solar azimuth and elevation in real-time and it is used to derive the relative position between the antenna beam pointing and the sun for each recorded data point.
We have revised our manuscript and please check the section 2.2.
Point 3: Did the authors perform several scans under different conditions and/or solar elevation angles for morning/noon/night? (e.g. summer/winter, morning/noon)?
Response 3: This method can be repeated under different solar elevation (25°ï½ž79°) and seasons. We observed and recorded data every 10 minutes and the sun is observed for more than 3 hours a day and the solar observation was typically performed once or twice a week. The sun was observed for more than 3 hours at noon (solar elevation>25°). However, the sun observation at low elevations should be avoided, especially in the evening and in the morning. Because the effect of atmospheric refraction and the side lobes of antenna beam are more obvious.
The description above has been added to the manuscript. Please check the section 4.3 and 4.4.
Point 4: How did the authors get the “daily mean” beamwidth, gain, and aperture efficiency as shown in Figs. 7 and 8?
Response 4: During the observation, the solar radiation collected over a certain period (typically solar elevation > 25°) is analyzed. We observed and recorded data every 10 minutes and the sun is observed for more than 3 hours a day and the daily mean and the standard deviation are calculated. The solar observation was typically performed once or twice a week from December 2019 to January 2021.
We have advised our manuscript. Please check the first and second paragraphs of the section 2.2 and 4.3.
Point 5: The authors recommend this method being applied routinely. However, it requires clear-sky conditions. Just like shown in Figs. 7 and 8, there are not many days satisfied clear-sky condition in 15 months. Therefore, how to compensate for such rigid conditions in order to apply this method routinely?
Response 5: Due to the spatial variations of the cloud and the horizontal inhomogeneity of the wate vapor, a large observation uncertainty is produced under cloudy-sky conditions, specially the middle and low cloud. According to our experiment, the effect is smaller for high cloud. Therefore, this method is feasible under the high cloud condition. In addition, we did not observe the sun every day and the observations are typically performed once or twice a week on sunny days.
The description above has been added to the manuscript. Please check the section 2.2 and 4.3.
Point 6: The meaning of section 4.4 “The effect of atmospheric refraction” is unclear.
Response 6: We have advised this manuscript. And please check the section 4.4.2.
Point 7: Figures are not ordered sequentially.
Response 7: These Figures have been checked and corrected.
Detail Comments:
Point 1: Line 47: missing “the” in front of “last few”
Response 1: We have corrected according to the suggestion.
Point 2: Line 50: “generally” should be “general”
Response 2: We have corrected according to the suggestion.
Point 3: Line 54, 55: “modelled” should be “modeled”
Response 3: We have corrected according to the suggestion.
Point 4: Line 130: please spell out “PPI”
Response 4: PPI: Polar Plane Indicator. We have corrected this part according to the suggestions.
Point 5: Line 133: please spell out “RHI”
Response 5: RHI: Range Height Indicator. We have corrected this part according to the suggestions.
Point 6: Line 166: “to use” should be “using”
Response 6: We have corrected according to the suggestion.
Point 7: Line 174: “an elevation” should be “and elevation”
Response 7: We have corrected according to the suggestion.
Point 8: Line 186: how much will the “angle distortion” affect the method?
Response 8: We have evaluated the effect of the distortion for the azimuth in the sky-sphere. The result is shown in Figure 3. It can be seen that the distortion is small for low-elevation and it is more obvious with a large rotation angle of the antenna in azimuth.
The description above has been added to the manuscript. Please check the section 3.2 and Figure 3.
Point 9: Line 192: please explain “other effects”, and how much will they affect the uncertainty
Response 9: These effects include antenna efficiency, a misalignment between the horn and the parabolic reflector, the non-uniform distribution of the solar TB. In general, these effects can be ignored according to the literature.
The description above has been added to the manuscript. Please check the section 3.3.
Point 10: Line 199. “However, it can be calculated by observing the sun”. Could the authors add more explanation and references?
Response 10: The effective area of the antenna is typically around 50%～60% of the physical area, it is a function of the feed horn and it is usually very difficult to determine. The popular method is to use the identical antennas to calibrate and measure the effective area in a microwave anechoic chamber and it is complex. However, the effective area can be easily measured by the sun-based monitoring method in operational, field applications after installation.
The description above has been added to the manuscript. Please check the last paragraph of the section 3.3.
Point 11: Line 223 and 232: “least squares” should be “least-square”
Response 11: We have corrected according to the suggestion.
Point 12: Line 241: missing “on” in front of “the point”
Response 12: We have corrected according to the suggestion.
Point 13: 3, 4, and 5: what is the time stamp for this experiment?
Response 13: The observation time is on March 14, 2020, 13:00 (local time). The time stamp has been added to the manuscript. Please check the Figure 3, 4, 5.
Point 14: Line 262: missing “a” in front of “small bias”
Response 14: We have corrected according to the suggestion.
Point 15: Line 268: “a slightly offset is still seen in the center”. Could the authors quantify the value of the offset? “slightly” should be “slight”
Response 15: The pointing bias data exhibit a slight offset is still seen in the center, the mean azimuth and elevation could be determined with 0.17° and 0.1°. We have corrected this part according to the suggestion.
Point 16: Line 272: redundant “of” in front of “between”
Response 16: We have corrected according to the suggestion.
Point 17: 7 and 8: How many days are included in these two figures?
Response 17: Measurements were taken on a total of 53 days from December 2019 to January 2021.
The description above has been added to the manuscript. Please check the Figure 7 and 8.
Point 18: Line 313 and 319: “in field” should be “in-field”
Response 18: We have corrected according to the suggestion.
Point 19: Line 329: redundant “the” in front of “Figure 9”
Response 19: We have corrected according to the suggestion.
Point 20: Line 330: missing “the” in front of “radiative”
Response 20: We have corrected according to the suggestion.
Point 21: Line 339: “an extension of the method”. Could the authors justify this statement?
Response 21: We have revised this part according to the suggestion.
Point 22: Line 352-353, “In the daily average system…” Please rephrase this sentence.
Response 22: We have revised this part according to the suggestion.
Point 23: Line 359: “independent” should be “independently”
Response 23: We have corrected according to the suggestion.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors did a very good job responding to all my questions/comments.
