Enhancing Communication Reliability: Designing Microwave Links for Bahir Dar-Woretta Connectivity

. Tis paper explores the need for establishing a microwave link between Bahir Dar and Woretta as an alternative communication solution to the existing optical fber infrastructure. Microwave links ofer an efective way to overcome challenges posed by rugged terrains and unfavorable environmental conditions that hinder the deployment of fber optics. As Woretta emerges as a key economic and investment hub within the Amhara Region, demand for reliable and efcient communication is expected to grow signifcantly. Te study encompasses various aspects of planning and designing the microwave link, including site surveys, consideration of fade margins, frequency planning, link budget calculations, and assessing the feasibility and reliability of the proposed link. Te paper employs LINKPlanner 5.4.1 software to simulate and validate the results. Due to terrain constraints, a direct link between Bahir Dar and Woretta is not feasible. Instead, a two-hop link is proposed, involving transmission from Bahir Dar to Zege, and then from Zege to Woretta. Tis alternative confguration ensures optimal connectivity while addressing the terrain limitations. By presenting a comprehensive analysis and simulation of the microwave link, this paper provides valuable insights into the planning and implementation of a robust communication infrastructure. Te proposed microwave link will ofer a reliable and efcient alternative to the existing optical fber network, ensuring uninterrupted connectivity to support the region’s growth and development.


Introduction
Microwave links are of signifcant importance in the Amhara Region of Ethiopia due to the unsuitability of wired communication systems in most geographical areas [1].Tese links are commonly utilized for short-range indoor communications, telecommunications, and connecting remote and regional telephone exchanges to larger (main) exchanges, eliminating the need for copper or optical fber lines [2,3].Microwave frequencies are valuable for both terrestrial and satellite communication systems, including fxed and mobile setups.In the case of point-to-point radio links, antennas are installed on towers or other tall structures at adequate heights to establish a direct, unobstructed lineof-sight (LOS) path between the transmitter and receiver sites.
Designing a microwave link involves a methodical and systematic process, which can sometimes be timeconsuming.It encompasses various activities such as site surveys, calculations for loss/attenuation and fading, determination of fade margins, frequency planning, interference calculations, and assessments of quality and availability, as depicted in Figure 1.Te entire process is iterative and may undergo multiple redesign phases until the desired levels of quality and availability are achieved [3].

Microwave Link from Bahir Dar to Woretta
Te proposed terminal sites for the microwave link are Bahir Dar and Woretta, as indicated on the map shown in Figure 2.Both terminal points already have existing towers; however, there is currently no microwave link established between these two sites.
To establish a link, we measured the coordinates of the two sites using Global Positioning System (GPS) receivers.We then determined the possible hop distance using LINKPlanner 5.4.1 and Google software, which takes into account the coordinates [4,5].Table 1 shows the coordinates and possible hop distance of the proposed link.
Note that the specifc values for latitude, longitude, and hop distances should be flled in according to the measurements and the simulation results.
2.1.Path Profle from Bahir Dar to Woretta.Te path profle of the proposed microwave link depicts the visual representation of the route taken by radio waves between Bahir Dar and Woretta.Te path profle is generated using LINKPlanner 5.4.1 software with the integration of Google Earth, which utilizes the data collected from Table 1 [4,5].Tis profle illustrates the maximum distance between hops, as well as the elevation of both sites.Furthermore, it displays the elevation and distance of any obstacles encountered along the path.Refer to Figure 3 for a visual representation of the path profle.
Based on the path profle depicted in Figure 3, it is evident that there is an obstacle situated between Bahir Dar and Woretta.Te obstacle has an elevation of 1952 m and is located at a distance of 27.074 km from Bahir Dar, while its elevation is measured at 1950 m and it is situated 28.933 km away from Bahir Dar.Te obstacle's signifcant elevation creates a hindrance as there is no clear LOS between the two radio terminals.Consequently, the obstacle obstructs the transmission of radio waves between Bahir Dar and Woretta.Moreover, the elevation diference between the frst site (Bahir Dar) and the obstacle amounts to 149.6 m.Tis indicates that in order to establish a clear line of sight, a tower height of approximately 150 m would be required, in addition to the height of the trees.However, such a solution is impractical and not recommended.
Terefore, the most suitable resolution for this issue would be to seek an alternative path that incorporates a repeater station.Two potential alternative links are Bahir Dar to Zege and Zege to Woretta, which would enable the successful transmission of radio waves without being obstructed by the existing obstacle.

Link: Bahir Dar to Zege and Zege to Woretta
Te alternative path considered for analysis consists of two hops: one from Bahir Dar to Zege and another from Zege to Woretta, with a repeater located at Zege.Additionally, by implementing an Add and Drop Multiplexer (ADM) equipment at Zege, we can add/drop data, voice, and video services, thereby establishing an alternate link to Zege as well.Figure 4 illustrates the map displaying the alternative links comprising the two hops.
Te coordinates of the two hops, including latitude, longitude, and elevation, were determined by utilizing Global Positioning System (GPS) receivers at the existing towers.Te specifc measurements are provided in Table 2.

3.1.
Path Profle from Bahir Dar to Zege.Te maximum distance between the two terminals in the hop is 12.7 km.Although there are no obstacles due to Lake Tana between these terminals, there is no clear LOS due to the height of the trees at both locations.To achieve a clear LOS, antennas are needed for the wireless connection.To ensure that they are above tree level, they need to be installed on tall towers.
Te path profle of the link between the two sites was analyzed using LINKPlanner 5.4.1 and Google Earth software [4,5], based on the data provided in Table 2. Te analysis results are displayed in Figure 5.In Figure 5, the red line represents the clear line of sight, while the blue line indicates the FFZ.To ensure a clear line of sight, the red line must be within the blue lines (FFZ).Advances in Materials Science and Engineering 19.498 km from Zege, with maximum elevations (heights) of 1847.9 m and 1884.6 m, respectively.Te path profle of this link was generated using the data provided in Table 2 and analyzed using LINKPlanner 5.4.1 and Google Earth software [4,5].

Path Profle from
In Figure 6, it can be observed that the Zege terminal has a higher elevation than the obstacle height, while the Woretta site has a lower elevation than the obstacle.Due to the presence of the obstacle, the link does not have a clear LOS.However, this issue can be resolved by utilizing antennas with sufcient height at both terminals.
In Figure 6, the red line represents the clear LOS, while the blue line indicates the FFZ.For a clear LOS, the red line must be within the blue lines (FFZ).
Note.From the two fgures, it is evident that both links do not have a clear LOS.Terefore, in order to establish a reliable microwave link communication, it is necessary to

Frequency Planning
Te operating frequency of the microwave link is chosen based on the operating frequency of the existing link in the direction of the proposed link and the hop distance.Tis is done to prevent interference and minimize path loss.In this case, the existing link at Bahir Dar station operates at a frequency band of 4 GHz.Terefore, the frequency selected for the new link should be diferent from this band.For our design, we have opted to use the 7 GHz frequency band.Te frequency bands of the frst and second hop are arranged and presented in Table 3. Tese frequencies have been carefully selected to ensure efcient and interference-free communication along the proposed microwave link based on ITU-R [6].
Considering the frequency bands mentioned above for the proposed link, the frequencies for both hops in the upper and lower bands are arranged as follows: the duplex frequency is set at 154MHz, a guard band of 3MHz is allocated, and the center band spans 14MHz.
Te upper and lower frequency bands for the frst hop are 7722 MHz to 7582 MHz which is used for the link from Zege to Bahir Dar and 7428 MHz to 7568 MHz which is used for the link from Bahir Dar to Zege, respectively.
For the second hop, the upper and lower frequency bands are 7282 MHz to 7422 MHz which is used for the link from Woretta to Zege and 7268 MHz to 7128 MHz which is used for the link from Zege to Woretta, respectively.By arranging the frequencies in this manner the higher frequencies are transmitted from Zege, which helps avoid conficts in terms of high/low frequencies at Zege site.

First Fresnel Zone (FFZ) Calculation
In a feasible link, it is desirable to have at least 60% of the FFZ free from any type of obstruction along the communication path.Te size of the FFZ depends on the distance between the transmitter and the receiver (known as the hop distance) as well as the operating frequency.Te maximum radius of the FFZ can be calculated using the following formula: Range on path (kilometers) When obstruction occurs between the two terminals, the frst Fresnel zone is calculated by [7][8][9] where F 1 = frst Fresnel zone radius in meters, d 1 = distance of P from one end in km, d 2 = distance of P from the other end in km, and It is important to note that this formula assumes a clear LOS between the transmitter and the receiver.If there are any obstacles or obstructions along the path, the size of the FFZ may be reduced, leading to potential signal degradation or interference.

FFZ: Bahir Dar to Zege.
Te maximum 60% FFZ radius of this path is calculated using equation ( 1) where d = distance from Bahir Dar to Zege in km = 12.7 km and f = operating frequency of the link = 7.425 GHz.
Based on the given information, the FFZ radius of the hop from Bahir Dar to Zege is 11 m, which represents 60% of the FFZ radius.Te FFZ radius, as shown in Figure 7, is free from any obstructions and meets the criteria for microwave link design.2) and considering the following parameters: the operating frequency of the link (f � 7.125 GHz), the distance from Zege to the obstacle (d 1 � 19.5 km), and the distance from the obstacle to Woretta (d 2 � 26.9 km), the 60% radius of the FFZ for the given link can be determined.

FFZ: Zege to Woretta. Using equation (
Based on the given information, it is stated that there is a clear LOS between the two sites, and 60% of the FFZ is free from any obstructions.Te FFZ radius from Zege to Woretta is shown in Figure 8.

Antenna Height Calculation
Te antenna height of the microwave link is calculated based on Rec.ITU-R P.530-14.For the frst hop, the antenna height (A h ) is calculated as 1.0 times the FFZ radius (F1), which results in 1 * 11 m � 11 m.We must consider the height of trees (15 m) and the growth of vegetables (3 m).
Terefore, the minimum antenna height for the frst hop is For the second hop, the antenna height (A h ) is calculated as 1.0 times the FFZ radius (F1) plus 15 m, resulting in 1 * 21.6 m + 15 m � 36.6 m.Tis is the minimum antenna height for the second hop.In both hops, the antenna should not be mounted at a height less than the calculated values.
In our design, the antennas can be mounted at 35 m and 40 m for the frst hop and the second hop, respectively, on the existing tower heights to provide more clearance.Te frst and second hop path profles with the recommended antenna heights (35 m and 40 m) are shown in Figures 7 and  8, respectively.Tese fgures indicate that the link is feasible and there is a clear LOS for both links (Bahir Dar to Zege and Zege to Woretta).

. Microwave Link Path Analysis
Te path analysis (or link budget) is carried out to measure the link.It is a calculation involving the gain and loss factors associated with the antennas, transmitters, transmission lines, and propagation environment, to determine the maximum distance at which a transmitter and receiver can successfully operate.
7.1.Free-Space Loss.Free-space loss (FSL) is always present, and it is dependent on distance and frequency.Te FSL between two isotropic antennas is derived from the relationship between the total output power from a transmitter and the received power at the receiver.After converting to units of frequency and expressing it in the logarithmic (decibel) form, it can be calculated using the following equation: [7,10,11] where f = frequency (GHz) and d = LOS range between antennas (km).

Received Signal Level.
Te received signal level (RSL) is the power level entering at the frst active stage of the receiver.In most cases since the same duplex radio setup is applied to both stations, the calculation of the received signal level is independent of direction.RSL can be calculated by the following formula: where RSL ≥ Rx (receiver sensitivity threshold), P t = output power of the transmitter (dBm), L ctx = loss (cable, connectors, and branching unit) between transmitter and antenna (dB), L crx = loss (cable, connectors, and branching unit) between receiver and antenna (dB), G atx = gain of transmitter/receiver antenna (dBi), and FSL = free-space loss (dB).

Rain Attenuation Calculation
Rain attenuations are considered one of the factors that decrease the magnitude of the received power in microwave link, so it must be considered in link budget analysis by collecting the rain rates at the selected site of the link.For our design, rainfall rate data for a 23-year period in Bahir Dar, as well as 30-year data for Zege and Woretta, were gathered from the National Meteorology Agency of Ethiopia.

Rain Attenuation Calculation for the First Hop (Bahir Dar to Zege
). Te rain attenuation calculations are calculated based on ITU-R Model of Rain Attenuation because the rain attenuation is minimum in this model when compared to other methods.It is calculated by using the following steps [12].
Step 1: Obtain the rain rate R 0.01 exceeded for 0.01% of the time (with an integration of 1 min).In Bahir Dar, the monthly rain in mm is 1840 and based on ITU-R P.837-6, the rain rate is 57 mm/h [13,14].
Step 2: Compute the specifc attenuation, c (dB/km) for 7 GHz frequency band, vertical polarization, and the above rain rate.It can be described as follows: where Υ = rain rate at p% probability and k, α = functions of frequency, f (GHz), in the range 1 to 1000 GHz.Te specifc attenuation is computed based on ITU-R P.838-3 for 7 GHz frequency using k = 0.00265 and α = 1.312 [7,15].Te calculation is done by using equation (7) as follows: Step 3: Compute the efective path length d eff , of the link by multiplying the actual path length (d) by a distance factor r. Before computing efective path length we must calculate distance factor r given by [8] where d is path length in km and f is frequency in GHz.Based on the above equation, by using d = 12.7 km and f = 7 GHz, the distance factor can be determined by using equation (9).
Step 4: An estimate of the path attenuation exceeded for 0.01% of the time is given by [8] A 0.01 � cd eff � Υd.r dB.
By using the values of distance factor and specifc attenuation from the above analysis, the estimated path attenuation exceeded for 0.01% is calculated by using equation (11).

Rain Attenuation Calculation for the Second Hop (Zege to Woretta).
Te rain attenuation calculations are calculated based on ITU-R Model because the rain attenuation is minimum when compared to other methods [12].It is calculated by using the following steps.
Step 2: Compute the specifc attenuation, c (dB/km) for 7 GHz frequency, vertical polarization, and the above rain rate.Te specifc attenuation is computed based on ITU-R P.838-3 for 7 GHz frequency using k = 0.00265 and α = 1.312 [7,15].Te calculation is done by using equation ( 7) as follows: Step 3: Compute the efective path length, def, of the link by multiplying the actual path length (d) by a distance factor r. Before computing efective path length, we must calculate distance factor r by using equation ( 9) [8].Based on equation (9), by using d = 46.4km and f = 7 GHz, the distance factor becomes r � 0. 323.
Step 4: An estimate of the path attenuation exceeded for 0.01% of the time is calculated by using equation (11).
Te rain attenuation of the second hop is greater than the frst hop because the hop distance and rain rate are greater.Rain attenuation is directly proportional to the rain rate and path length.

Fade Margin
Fade margin is the diference between the receiver's signal level at full strength and a receiving antenna's sensitivity.In the propagation path, determining sufcient fade margin is the most important step in microwave link design.If the margin is too small, the link will be unstable; as a result, sufcient availability of the link or quality of the provided services cannot be guaranteed.
A wide fade margin helps to assure link availability in case the signal is weak.Fade margin is calculated as follows [16,17]: where FM = Fade Margin (dB), RSL = Received Signal Level (dBm), and RS = Receiver Sensitivity (dBm).

Link Budget Calculation of the Recommended Link
Te recommended link has two hops.Te link budget is calculated to know the reliability of the link to be designed by selecting diferent equipment with the appropriate rating [16].Te specifcation of the equipment used at the transmitter and receiver site is shown in      6) using the following data.L ctx � 5.7 dB + 0.025 dB � 5.725 dB; because the cable length at the transmitter side is 60 m, it has 5.7 dB loss and 0.025 is connector loss between transmitter/receiver and antenna (dB).
L crx = 5.7 dB + 0.025 dB = 5.725 dB; because the cable length at the transmitter side is 60 m, it has 5.7 dB loss and 0.025 is connector loss between transmitter/receiver and antenna (dB).Te FM of the second hop is also greater than the recommended FM values (10 dB), so it indicates that the link is reliable but degree of reliability is less than the frst hop.

Interference Prediction
When an unwanted signal is picked up by a radio receiver, it is known as interference.Tese interfering signals can originate from various sources.One of the most common types of interference sources is related to frequency planning, which can lead to issues such as insufcient bandwidth adherence, improper installation, outdated equipment, and the unwanted (interfering) signal from the interfering links.
Te ratio of the desired signal to the unwanted (interfering) signal can be determined by considering the power received from the desired link and the interfering signal from the interfering transmitter that may enter the receiver.
Te wanted signal S at the connector point of the receiver antenna is calculated as [20] S[dBm] � P RX,S � P TX,S + G TX,S + G RX,S − FSL S − L S , (23) where P TX,S is the transmitted power of the wanted signal, G TX,S is transmitter antenna gain compared to the isotropic one, given in dBi units, G RX,S is the receiver antenna gain compared to the isotropic one, given in dBi units, FSL S in dB is the free-space loss of the victim path, and L S in dB units refects other propagation losses such as obstacles in the victim path, e.g., buildings, power pylons, or trees.Due to interference, the victim path may experience degradation in the bit error rate (BER), and it becomes challenging to maintain long-term availability targets.Te power level of the interfering signal, P RX,I , received at the antenna connector point of the victim receiver can be calculated as follows [20]: where P TX,I is the power emitted by the interfering transmitter, G TX,I is interferor transmitter antenna gain compared to the isotropic antenna gain, given in dBi units, G RX,S is the antenna gain of the victim receiver compared to the isotropic one, given in dBi units, Discr is the total antenna (spatial) discrimination, in dB, FSL I is the free-space loss in the interference path, and L I refects other losses in the interfering path, e.g., obstacles, buildings, power pylons, or trees.Spatial discrimination is depending on the following three main factors: θ S gives discrimination due to the angle between the main lobe of the victim path and the interference path, θ I gives the discrimination due to the angle between the main lobe of the interfering signal and the victim path, and V/H corresponds to polarization discrimination [20].Tese three factors collectively contribute to spatial discrimination systems.
Te signal to interference ratio is calculated then from the equations ( 22) and (23) In our design, both links interfere with each other and potentially afect other links in the vicinity of each site.However, the level of interference in the proposed link is minimal due to several factors.Firstly, the link has been equipped with sufcient bandwidth to accommodate the desired signal without signifcant degradation.Additionally, careful frequency planning has been implemented to minimize the chances of interference from other sources.Lastly, the use of new radio equipment ensures optimal performance and reduces the likelihood of interference.
Advances in Materials Science and Engineering

Link Reliability (Performance) Evaluation
Te path availability (also called link reliability) is the percentage of time that the received signal is above the required threshold, P req .It is sometimes expressed as the expected minutes of outage per year.Te path availability is a function of the radio frequency, diversity (if any), fade margin, path length, and local climate.
Te International Telecommunication Union publishes reports with empirical models of required fade margin for diferent parts of the world.Te percentage of time represents the outage time for a given link budget [17].
Te calculation of the percentage of time (p w ) in which the fade depth (A) (in dB) is exceeded during the average worst month is performed using the following equation [7].
where k = geoclimatic factor, d = path distance in km, f = frequency in GHz, and A = fade margin in dB.Te path inclination |ε p | (mrad) of the link is calculated from the antenna heights of the transmitter and receiver (m above sea level or some other reference height), and it is calculated as follows [5,7,17]: where h A = antenna height + ground elevation at transmitter, m, and h B = antenna height + ground elevation at receiver, m.Geoclimatic (k) factors are an additional parameter that determines the percentage of time for the average worst month.It can be calculated using k � 10 − 5.9− C Lat − C Log  PL 1.5 . ( Te aforementioned link equation is utilized due to the proposed link traversing medium-sized bodies of water, including a portion of Lake Tana.In accordance with ITU recommendations, the calculation of the geoclimatic factor (k) involves four categories, two for land links and two for over-water links.Estimation of k can be carried out by referring to contour maps provided in Figures of ITU-RPN.453-4,specifcally Figures 7 and 8. Tis estimation is based on the percentage of time (PL) during which the average refractivity gradient in the lowest 100 m of the atmosphere is below 100 N-units per km [10].
Te value of PL is determined using fgures from ITU-R PN.453-4.According to these fgures, the values of PL are determined to be 5, 20, 10, and 1 for the months of November, August, May, and February, respectively.To determine the fnal value of PL, we select the highest value among these, which is 20.Additionally, we take 0 dB as the value of C Lat and 0.3 dB as the value of C Lon .We can calculate the result by using equation (28).k � 10 − (5.9− 0− 0.3) 20 And we use fade depth (A) = 47 dB and percentage of time (p w ) by using equation (26).
We can consider that the above outage (unavailability) is due to propagation outage.
Te availability of this link is determined based on the outage of the worth month or time percentage and it can be calculated as follows.
(33) Advances in Materials Science and Engineering From the above unavailability and availability values, we can say the link is reliable.
12.2.Link Reliability from Zege to Woretta.To calculate the reliability or availability of this link, we take the same procedures and k values of the frst hop.Simply, we determine the inclination of path by equation ( 27 Te calculation of the percentage of time for the worst month is determined using equation (26), wherein the fade depth (A) is specifed as 32 dB.
Te cause of this outage (unavailability) appears to be a propagation issue in the frst hop.Upon analysis, it is evident that the outage in the second hop is more signifcant than that in the frst hop.
Te availability of this link is determined by calculating the outage percentage over a specifc period, such as a month, and can be computed as follows.
Link availability p A % � 100% − p w % � 100 % − 0.0001% � 99.9999%. ( Based on the provided unavailability and availability values, we can conclude that the link is reliable.However, its reliability is lower compared to the frst hop due to the high propagation loss.

Conclusion
Initially, a direct microwave link between Bahir Dar and Woretta was proposed due to the economic signifcance of Woretta as a growth center in the Amhara Region.However, Figure 3 reveals that there is a high-elevation obstacle along the path between the two sites, preventing the realization of this direct link due to non-line-of-sight (NLOS) propagation.Consequently, an alternative proposal involving a twohop connection from Bahir Dar to Zege and from Zege to Woretta was considered.Te link's path budget, free-space path loss, rain attenuation, fade margin, and reliability were calculated and simulated.Te results align with practical expectations.
Te path profles and frst Fresnel zone (FFZ) radii of the two-hop link, without antenna and with antenna heights of 35 m and 40 m, are depicted in Figures 5-8 for the frst and second hops, respectively.Tese illustrations demonstrate that there are no obstructions impeding line-of-sight or afecting the FFZ radius.In other words, the feasibility of the two-hop links is confrmed.
Te link availability of the two-hop connection was calculated based on ITU recommendations, resulting in a 99.9999999437% availability in the frst hop and 99.9999% in the second hop, with a negligible outage or unavailability percentage of 0.0000000563% in the frst hop and 0.0001% in the second hop.Te fade margin exceeds the recommended values, with 47 dB in the frst hop and 32 dB in the second hop.Tese values indicate that the designed link is highly reliable, ensuring the establishment of a quality service.Te percentage availability and fade margin provide assurance of the link's quality and reliability, guaranteeing interferencefree communication [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37].

Figure 2 :
Figure 2: Map of area of interest.

Figure 4 :
Figure 4: Te hops from Bahir Dar to Zege and from Zege to Woretta.

Figure 7 :Figure 8 :
Figure 7: Path profle between Bahir Dar and Zege with antenna height of 35 m at both sides.

( 19 )
Te link margin of the link designed from Bahir Dar to Zege is greater than 10 dB, and hence the communication established in this link is reliable and guaranteed.10.2.Link Budget Calculation fromZege to Woretta 10.2.1.FSL.Te free space of the above link is calculated by using the hop distance between Zege and Woretta and the selected operating frequency.And equation (5) is used to calculate FSL.f � frequency (GHz) � 7.125, d � LOS range between Zege and Woretta (km) � 6.375, L FSL � 92.45 + 20 log(7.125)+ 20 log(46.4)[dB],L FSL � 92.45 + 17.0556 + 33.326, L FSL � 142.8 dB.
-line-of-sight GPS: Global Positioning System.

Table 1 :
Proposed link coordinates and possible hop distance.

Table 2 :
Coordinates of hop between Bahir Dar to Zege and Zege to Woretta.

Table 3 :
Frequency bands for each hop.

Table 4
[18,19].10.1.Link Budget Calculation from Bahir Dar to Zege.In order to calculate the link budget, we use the specifcations of the equipment given in Table4.(17)10.1.2.RSL.It is the amount of power reached at the receiver unit and can be evaluated by using link budget parameter values specifed in Table4and the free-space loss.It can be calculated by using equation (6), based on the following parameter ratings.

Table 4 :
Specifcations of equipment used at transmitter and receiver site.It is the amount of power reached at the receiver unit, and it can be calculated by equation ( 1.5 � 2.247 * 10 − 4 . (29)12.1.Link Reliability from Bahir Dar to Zege.After we determine geoclimatic factors, path inclination will be calculated by using equation (27) with h A = 1837.4m, h B = 2016.4m, and Path Length (d) = 12.7 km.