Evaluation of Low-Cost Radiometer for Surface Reflectance Retrieval and Orbital Sensor’s Validation

Round 1

Reviewer 1 Report

I think this paper is appropriate to be published. The following comments may be considered for betterment.

1) The term "bias" should be used with "standard deviation" or "variation". The "bias" in this report is not fixed for a long term.

2) Between line 589 and line 602, the description is "ratio", however, the figure and table are "difference". The terminology difference between "ratio" and "difference" should be corrected. This part is an essential of this paper. Formula 10 is also “difference”.

3) The more explanation is necessary for the meaning of "before" and "after" in Figure 9 and Table 2.  I cannot understand,

4) The performance of each Arable sensor measured in the laboratory before the shipment should be described, such as spectral stability, temperature and humidity dependence, individual difference, so on.

5) The calibration interval and results of Arable sensors should be described. These results would give the confidence to this report.

6) More detailed uncertainty should be analyzed in chapter 4 because many other factors are discussed in chapter 5, such as down-welling radiance estimation accuracy, cloud and aerosol contamination effects, spectral response uncertainty, many Arable sensor is assumed as a single platform ... so on. Repeatability or Noise are not main issue. The main issue of this type of calibration is system error, I think.

7) SWIR bands topic is interesting; however, it should not be discussed in the same table. I think this topic is just a reference purpose.

8) The wavelength of Figure 8 should be described. Is it 870nm?

9) Formula 7 should be modified because the same Gain term appears twice.

10) There are two "chapter 5".

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

This work deals with a low-cost radiometer device used for surface reflectance accuracy evaluation. It shows promising capabilities to validate the retrieved multispectral SR products after being calibrated by ASD measurements. The author described in detail the measurements, cross-calibration, and uncertainties. It is a worthwhile evaluation to support the SR validation campaign by using such kind of low-cost radiometer worldwide. The work was interesting as whole and good writing. I only pointed out minor concerns as follows:

 1. Apart from the low-cost measurements like Arable, there were other relevant in-situ measurement sites, such as the RadCalNet, AERONET, FluxNet. Please add their helpfulness to validation SR in the introduction section. It is also important provide general comparison between the low-cost level and the expensive instruments deployed of sites like at RadCalNet.

 2. The surface homogeneity is required at the selected site to validate the satellite retrievals. In Figure 3, the rectangular blue measured region by ASD seems somewhat inhomogeneous from the image. If not, it is not suitable to use the averaged reflectance from ASD to calculate the  SBAF.

 3. Please add the cartography elements to Figures 1 and 3(a), such as north arrow and scale.

 4. Line 45, it is better to change the order of “ absorb or scatter “  into “ scatter or absorb “ to correspond the following “ aerosol, ash…” and “ gases…”.

 5. Please clarify the specific term “reflectance unit” in the manuscript. I guess it means 0.01 if I was corrected.

 6. The ASD measured reflectance at the North Airport Base was described in section 2.3. However, it is not clear that other vegetation types (Figures 2(a) and (b) ) were measured similar to North Airport Based and applied to Arable Mark 2 measurement correction respectively. Or you just used the measurement from the North Airport Base to all the sites. Please clarify.

 7. In section 5.3, please clarify the time difference between the OLI acquisition and Arable Mark measurement and how did you compensate the temporal differences.

 8. The selected sites were covered by vegetation. Do you have measurements from other surface types to further support the conclusions?

Author Response

Please see the attachment.

Author Response File: Author Response.docx