Performance Evaluation of VTEC GIMs for Regional Applications during Different Solar Activity Periods, Using RING TEC Values

Round 1

Reviewer 1 Report

The presentation lack almost of any physical explanation. 

For instance, is there any physical difference when examine quiet (HSS-induced storms) and disturb conditions (CNE-induced conditions) during HSA or LSA. I think no. Which is the reason of a sparate examination?

Some more questions have been noted on the manuscript.

Comments for author File: Comments.pdf

Author Response

All the answers to reviewer are in the attached file and in the manuscipt revised

thanks

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript nicely describes a study that compares two different ionospheric TEC techniques, the large scale GPS Global Ionosphere Maps (GIMs) and the regional “calibration technique” developed by Ciraolo et al. (2007). The results show how the differences between the GIM and Ciraolo et al. methods depend on the level of geomagnetic disturbance and latitude. Also, they find that the GIM TEC values are always larger than the Ciraolo et al. TEC values. These findings are very important for, and show the limitations of, studies that use GIM data for regional analysis. All researchers that use GIM data should read this paper, especially those that report regional TEC earthquake precursors when analyzing GIM data. I highly recommend prompt publication in Remote Sensing. 

Author Response

No answer required. The author thanks reviewer 2

Reviewer 3 Report

Review of paper “Performance Evaluation of VTEC GIMs for Regional Applications During Different Solar Activity Periods, Using RING TEC Values” by authors V. Tornatore, C. Cesaroni, M. Pezzopane, M. Alizadeh and H. Schuh.

 

This paper is on a regional comparison of VTEC values obtained from Global Ionospheric Maps from IGS with VTEC values estimated using GPS observations from regional GPS-receivers. In the regional approach, the calibration technique described in Ciraolo et al. (2007) is used.

 

The paper is interesting and well written. The described theory and selected approach have however been applied in other papers, many of them mentioned in references. On the other hand, the presentation of results is quite creative and the results both fit with existing knowledge and give indications that will be of benefit to users of GIMs. Overall, I therefore think the paper is worthy of publication in Remote Sensing.

 

In the final paper I recommend that the authors clarify and discuss the following.

• The absolute level of TEC values from GIMs is fixed through the datum definition of the differential code biases (DCB). In the datum definition approach selected by IGS, the condition is that the sum of satellite DCBs should be zero. The authors should shortly discuss the DCB datum issue for both the GIMs and the Ciraolo-calibrated model. The results seen in fig. 1 and fig.2 is probably explained by the datum definition issue.
• The calibration approach (page 4) is not sufficiently described. To make the paper more self-contained, the authors should include
  • The relation between dual frequency GPS (GNSS) code & carrier phase observations and STEC.
  • Weighting approach applied in the “phase-leveled-to-code” method
  • How is the beta(arc) / arc-offset constants determined (in the text it is just written that a calibration is carried out……..)
  • Cycle slips will, if not being repaired, introduce new arcs. In the results section, the cycle slip issue is mentioned as a possible cause for anomalies seen in the results from a very active ionosphere. The authors should therefore shortly discuss cycle slips and how cycle slips have been handled in their processing.
• In line 139 it is written that RINEX-files containing GPS code and carrier phase observables have been acquired. Please also include information on frequencies and signals.
• In line 132 it is erroneously written that p ≥ 0 and q ≤ 1. This should be 0 ≤ p < 1 and 0 ≤ q  < 1. Please also include a short verbal description of p and q.
• On page1 it is written that there are seven IGS ionospheric analysis centers (IAACs). According to the official IGS webpage, there are however eight centers as Optima/Germany have recently been added.
• “Between the lines”, it can be read that the authors have used their own software in their processing. Please clarify the use pf processing software as well as details concerning data processing, i.e. processing parameters as which signals to be processed, elevation cutoff, weighting approach, data cleaning (outliers, cycle slips).

 

 

The overall quality of the English language is good. The authors should however make sure that they use a consistent font throughout the paper (see e.g. line 113-118). Below are a few examples where I recommend the authors to make alternations:

• Sentence in line 82-85
• Sentence in line 147-148
• In line 206 : “…that these estimates are more reliable …”. Please clarify the meaning of “these”.

 

 

Author Response

The answers are in the file attached.

The authirs thanks reviewer

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Please look some comments at the attached file

Comments for author File: Comments.pdf

Author Response

Please see the attachments

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

The manuscript was highly improved.  Adequate responses have been given to the reviewer's comments / queries. 

A short question. An addition of the quite (Q) and active (A) times of TEC gives a different total number in the 3 observatories. In particular, in RESU station: Q + A = 2937 in Fig. 2 and Q + A = 3479 in Fig. 1. I s this problem of the initial data set?

 

 

Author Response

The answer is in the attached file

kind regards and thanks

Author Response File: Author Response.pdf