Assessment of Terra/Aqua MODIS and Deep Convective Cloud Albedo Solar Calibration Accuracies and Stabilities Using Lunar Calibrated MERBE Results

Round 1

Reviewer 1 Report

to my view, the paper can be published with some minor corrections of the language. Unfortunately, the author often uses quite long sentences which are difficult to disentangle.

Author Response

Many thanks to this reviewer, I have gone through the manuscript and wherever possible shortened sentences, see lines: 18,25,31,4951,55,68,97,145,171,230,259.

Reviewer 2 Report

Good works for the assessment of albedo accuracies and stabilities using Lunar Calibrated MERBE results. This article is suggested to be accepted in present form.

Author Response

Many thanks to this reviewer.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

My review on the second version hasn’t changed from my first review on the first version. I pointed out that samplings of deep convective clouds from the first half and second half of the first version are different. The author revised in a way that the second version reads as if there is a separate topic. The manuscript therefore contains two topics, calibration of MODIS with MERBE and the stability of deep convective cloud albedo. Because the author used two different criteria selecting deep convective clouds, these are really two different topics. This is not what I suggested in my first review. The author needs to use a tighter screening of deep convective clouds for the first half too.

In the reply, the author mentions that absolute calibration and stability are different. The author implies that for stability calibration, a set of deep convective clouds with larger variability of albedos is acceptable. But the focus is on the stability in the second half too. Therefore, I am not convinced that the set is good enough to test the stability in the first half. In addition, the author does not distinguish albedo and radiance. Units used in Figure 2 is for radiance, not for albedo or irradiance. In addition, how the author derives albedo from the radiance is not explained at all. Furthermore, the author introduces ‘MERBE Watt’. I do not understand this concept from the descriptions given in the manuscript. For example, Equation 3 has integration only over wavelength. The author does not explain how the radiance is integrated over solid angle. In sort, I do not think that the author cleaned logical flaw I pointed out in the first review. The manuscript does not provide enough explanation. As a result, it is not a stand-alone paper that the reader can understand the method, results, and conclusions.

Reviewer 2 Report

Detection of a climate change impact on clouds is extremely challenging because of their huge natural variability. Satellite data are used to monitor such changes, but whether there are significant trends can only be stated if these data themselves are reliable and when the detection is temporally stable. Unfortunately, devices degrade over time and not all such effects are traceable by instrument-internal calibration devices. The author uses radiance data from lunar scans which are assumed to be stable to calibrate channels on Terra and Aqua MODIS. He furthermore demnstrates with these data that Deep Convective Clouds can be used with good accuracy as a radiation standard. Finally he shows that using these calibration possibilities it should be possible to detect cloud radiative forcing changes with statistical significance much earlier (~20 years) and with available data than expected by NASA using new instruments that are not yet in orbit.

I think this is a good paper, worth publication.
My main concern is that the paper is not easily understandable for people outside the satellite community. The author is encouraged to work on this aspect. Also the language needs to be improved as you can see from the long list of specific comments.   

Lines 47/48: "The SW CRF signals being looked for have been estimated to be only ±0.8%/decade or less in size of global albedo". This is unclear. I don't understand why the SW signal is measured in %/decade. To me this looks like a trend. Please reformulate.

Line 58: "false reflected solar trend" should be reformulated. I think "false trend of reflected solar radiation" is meant.

Line 62/63: "but since this is a cross-instrument/albedo comparison, it plays no relative factor". Please make "this" and "it" explicit. I don't know what you mean.

Line 64: "Climate observing instrument": I suggest to state the name of the instrument.

Line 70: "MODIS Percent albedo change stability per decade" is an involved expression. Is this the change of a stability or is the change (i.e. a rate) stable (i.e. more or less constant)?

Line 86: Please delete the word "existing".

Line 88: "0.8%/decade reflected solar signal". I have the impression you use the word "signal" for "trend". Maybe that is general use in the satellite community. But it would help to say it once in the beginning, e.g. in Line 48 (see comment above). Perhaps "signal (trend)" would already help. 

Lines 117/118: What does the "still present" in this sentence mean? Is is expected that these data will vanish soon?

Lines 136/137 and further below: Can you please exchange the "results" by something more specific. 

Eq. 1: Can you say more on the regression? How good are they? How large are the residuals? Why is a quadratic regression necessary? I think, such information is required in order to assess the claim that the Vmodis-V'modis is in the +-3% range.

Line 167: Again replace "result" by a physical notion.

Lines 170-173: There is much information involved in this long bracket. It is hard to understand. Please rewrite this passage. It is not necessary to put important information in brackets, so please avoid them.

Lines 176/177: "The one sigma absolute accuracy goal of MERBE is shown to perhaps be as high as 0.3%...". I don't understand this. A goal should be something defined, what then does the "perhaps" mean? So either the word "goal" or the word "perhaps" does not fit here.

Line 205: What is VZ?

Line 223: "but the used anisotropic radiance to flux lookup factors[35], are systematic": What do you mean? Please note that this paper should be understandable for more readers than just the innermost circle of MODIS experts.

Line 238: I think the word "functioning" can be deleted. 

Line 243: "orders of magnitude". Isn't this a bit exaggerated?

Figure 6 caption should be rewritten. To me it has no grammatical structure. A possibility could be to divide the sentence into two or three sentences. 

Line 260: "respectfully" or "respectively"?