Epoch-Wise Estimation and Analysis of GNSS Receiver DCB under High and Low Solar Activity Conditions

Round 1

Reviewer 1 Report

The manuscript presents an interesting and important issue which is the time variation of the receiver hardware delays. A proper understanding of its effects is still a research matter in the technique for modelling and estimating then, will benefit GNSS ionospheric studies and receiver clock corrections.

 

The authors propose a method that combined MCCL and ionosphere model to estimate the epoch-wise receiver DCB accounting for the potential time variation of the receiver hardware delays, and give a clear explanation on how the definition of a datum solves rank-deficient problem and also how the datum is estimated. This paper also analyse the possible reason of DCB instability under high and low solar activity conditions, which could help in the design of antennas and in fine-tuning the receiver GNSS signal processing modules.

 

The manuscript is well written and structured, with all the relevant information well explained. The set of measurements used are relevant and representative of the phenomena analysed. In my opinion, the paper could be accepted.

 

Two minor correction:

1.     As for DCB, some places are represented by ‘RDCB’, while others are represented by ‘receiver DCB’. It is suggested to use uniform notation.

2.     In 3.1 fourth paragraph, ’Red lines depict the BR-DCB estimates using SD-GF method (see Eq. (12))’. The ‘Eq. (12)’ is not exist. Please, check this point.

 

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Author Response

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Reviewer 2 Report

Differential code bias (DCB) has been one of the main errors in ionospheric total electron content (TEC) retrieval using global navigation satellite system (GNSS), eventually playing an important role in estimating the delays in trans-ionospheric radio propagation. In the retrieval of TEC, the satellite and receiver biases are crucial though the satellite biases are periodically estimated worldwide, the receiver biases are specific to the receiver and its location. In this regard, the authors have performed excellent work by reviewing the estimates of epoch-wise Receiver DCBs, for 200 Inter-national GNSS Service (IGS) stations in 2014 (high solar activity) and 2017(low solar activity). The results show that the proportion of intraday RDCBs stability increases from 72.5% in 2014 to 87% in 2017 which suggests the replacement of the receiver hardware in stations. The intraday variability of the RDCBs was confirmed to be related to the receiver environment temperature rather than the receiver firmware version.

The authors found that the significant variability in the estimates of the receiver DCBs over a one-day period shows good consistency with the intraday temperature variation. Finally, the manuscript concludes that temperature is one of the main factors affecting the intraday variability of receiver DCBs. The mathematical description and result analysis are sufficient. The figures are with good clarity. I think this paper may qualify for acceptance.

Author Response

Thank you very much for your support of our research. 

Reviewer 3 Report

The manuscript describes a method for estimating intra-daily differential code bias (DCB) variations. The algorithm is tested using simulated and real GNSS data of the IGS network covering two days in 2014 and 2017, respectively.

Overall, the study goal is clearly addressed and existing literature is sufficiently cited. However, the derived methodology is not very easy to follow. Thus, in the following a few suggestions (mainly in form of questions) are given to further improve the paper.

- Please derive the formulas in section 2 from the standard equation for DCBs: P_S1 - P_S2 = (I_S1 - I_S2) + (B_S1 - B_S2) with I_S1 - I_S2 = 40.31 * (1/f_S1^2 - 1/f_S2^2) * STEC and show how equation 1 is related to it.

- Please make more clear how you deal with the satellite DCBs. Do you introduce common values or do you estimate them together with the receiver DCBs? In case of estimation, how well do they agree with the CODE values?

- How reliable is the approach for estimating real ambiguities only at the first epoch? Can you provide any uncertainties?

- How do you deal with cycle slips?

- Table 1: 2010 or 2014?

- Last sentence on page 5: Not very clear, please rephrase

- Figure 1 caption: What exactly is shown in subplot c)?

 

Author Response

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