3. Detailed information

3-a. 3D electron density option

There are 3 options: “GNSS tomography” or “GAIA model” or “IRI model”.
*“GNSS tomography” is a default option.

• GNSS tomography: 3-D real-time ionospheric tomography over Japan based on GNSS observations
  https://www.enri.go.jp/cnspub/tomo3/
• GAIA: Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy
  https://gaia-web.nict.go.jp/index_e.html
• IRI: Widely used International Reference Ionosphere model. IRI-2016 model is used in the HF-START service.
  http://irimodel.org/

3-b. Target date and time (UTC)

You can set date and time (UTC) for calculation.
*The most recent date and time, which can be used in calculation, are set as default values. You can also click the “Latest” button to make sure that it is the most recent time for calculation. Date and time can be inputted freely in available data range.

3-c. Transmitting point for calculation

You can set transmitting point into fields.
*“Lon : 139.5,  Lat : 35.7” are set as default transmitting longitude and latitude. 
You can enter the transmitting point by numerical input of longitude and latitude or by selecting from major cities in Japan and the world. You can switch the format with the button at the top of the input field. **Selectable transmitting point differs between “GNSS tomography” and “GAIA model” and “IRI model” as shown in following table.

	GNSS tomography	GAIA model	IRI model
Tx lon [degree E]	128 to 147	-180 to 180	-180 to 180
Tx lat [degree N]	30 to 46	-90 to 90	-90 to 90

3-d. Transmission information and receiver point for calculation

You can set Transmission information and receiver point into fields, and these can be registered up to 10 sets by clicking “Set ray path” for the 1^st set and “Add ray path” for the 2^nd to the 10^th set. Registered set can be removed by clicking “X” mark.
Depending on the ON/OFF of the Ham radio mode, you can input it differently as written below. At each mode, it is also possible to input with multiple formats by selecting the preferred option at the top of each input field.

[When Ham radio mode is OFF]

• Transmission angle: You can enter zenith angle (degree) or elevation angle (degree) by numerical.
• Frequency: You can enter frequency (MHz) or wavelength (m) by numerical.
• Reciever point: You can enter the transmission point by numerical input of longitude and latitude or by selecting from major cities in Japan and the world.

When you open the web tool, “Zenith: 30”, “Frequency: 6.055”, ”Rx lon: 130.6”, “Rx lat: 31.2” are set as default.

[When Ham radio mode is ON]

• Transmission angle: You can enter launch angle (degree) by numerical.
• Frequency: You can chose from the list of commonly used frequency bands (MHz) / wavelengths (m).
• Reciever point: You can choose from major cities in Japan or DXCC entities.

When you open the web tool, “Launch angle: 60”, “Freq. band / Wavelength: 3.5MHz / 80m”, ”Hokkaido (@Sapporo)” are set as default.

**The available range for “GNSS tomography” ,“GAIA model” and “IRI model” are shown in following table.

	GNSS tomography	GAIA model	IRI model
Zenith angle [degree]	0 to 79.9	0 to 79.9	0 to 79.9
Elevation angle [degree]	10.1 to 90	10.1 to 90	10.1 to 90
Launch angle [degree]	10.1 to 90	10.1 to 90	10.1 to 90
Frequency [MHz]	3 to 30	3 to 30	3 to 30
Wavelength [m]	10 to 100	10 to 100	10 to 100
Rx lon [degree E]	128 to 147	-180 to 180	-180 to 180
Rx lat [degree N]	30 to 46	-90 to 90	-90 to 90

3-e. Error massages

Dialogue title	Dialogue massage	Meaning
Service Unavailable	Please try again later.	Server connection was failed.
No density data	Specified time's density data does not exist.	For some reason, specified time's density data does not exist.
Time-out Error	Your process has timed out.	Calculation request has timed out.
Error on processing program	Process ID: [ID]	Calculation request was failed on [ID].
This server is too busy	Please try again after a while.	Currently, the server capacity is overflown.
Internal Server Error	Unexpected error has occurred.	Unexpected error has occurred.

3-f. Propagation information

The propagation information is available for every Tx-Rx paths. Information from each Tx-Rx path is started with “Pathxx”, where xx is path number (i.e. 01-10). Zenith angle (degree) and azimuth angle (degree) of the first hop, Tx latitude (degree) and longitude (degree), Rx latitude (degree) and longitude (degree), and the frequency (MHz) are listed.

Next, the propagation information from each hop is listed. At each hop, “Refraction point” indicates the highest point [latitude (degree), longitude (degree), altitude (km)], where the radio wave refracts back from the ionosphere. “Propagation time” in milliseconds indicates the time when the radio wave propagates in 1 hop from one point to another point on the ground. “Next launch” indicates zenith angle (degree) and azimuth angle (degree) for launching the next hop. “Reach point” indicates the point [latitude (degree), longitude (degree), altitude (km)], where the radio wave reaches the ground. It is also the position where the next hop will be launched. “distance to destination” indicates the nearest distance on the ground from the reach point to the Rx.

When no more hop can propagate to the Rx, the message “No more hop is possible from now.” will be displayed. The “Max hop” indicates the maximum hop number that the radio wave can propagate from Tx to Rx. Only the ground-to-ground propagation is counted as 1 hop.

4. Reference

4-a. HF-START

• K. Hozumi, M. Ishii, S. Saito, T. Maruyama, H. Nakata, and T. Tsugawa, "HF-START: Application in Aid of Radio Communications/Navigation", In: Electronic Navigation Research Institute (eds) Air Traffic Management and Systems III. EIWAC 2017. Lecture Notes in Electrical Engineering, vol 555. Springer, Singapore, https://link.springer.com/chapter/10.1007/978-981-13-7086-1_19.　[Paper link]
• K. Hozumi, T. Kondo, S. Saito, H. Nakata, T. Maruyama, T. Tsugawa, and M. Ishii, "Low Cost Development of HF Receiver Prototype for HF-START Field Campaign", 2018 2nd URSI Atlantic Radio Science Meeting (AT-RASC), Meloneras, Spain, pp. 1-4. doi: 10.23919/URSI-AT-RASC.2018.8471477, 2018. (Young Scientist Award)　[Paper link]

4-b. GNSS tomography

• S. Saito, S. Susuki, M. Yamamoto, A. Saito, “Real-time ionosphere monitoring by three- dimensional tomography over Japan”, Inst Navig 64:495–504. https://doi.org/10.1002/navi.213, 2017.　[Paper link]

4-c. GAIA

• Tao, C., H. Jin, Y. Miyoshi, H. Shinagawa, H. Fujiwara, M. Nishioka, and M. Ishii, "Numerical forecast of the upper atmosphere and ionosphere using GAIA", Earth Planets Space, 72:178, https://doi.org/10.1186/s40623-020-01307-x, 2020.　[Paper link]

4-d. IRI

• D. Bilitza, D. Altadill, V. Truhlik, V. Shubin, I. Galkin, B. Reinisch, and X. Huang, "International Reference Ionosphere 2016: From ionospheric climate to real-time weather predictions", Space Weather, 15, 418-429, doi:10.1002/2016SW001593, 2017.　[Paper link]