Telecommunications, Navigation & Electronics

El 23 de julio no pude dormir, algo me dijo que me levantara. Salí al balcón, el cielo estaba despejado y todas las luces de los apartamentos cercanos estaban apagadas.

La luna no estaba del todo llena, pero era absolutamente hermosa a unos 128 grados. Entonces, de repente, lo vi solo. Al principio pensé que era un planeta, pero al revisar la tabla de estrellas era Capella.

Pude medir la distancia angular entre Capella y la extremidad cercana de la Luna:

Distancia lunar observada = 75deg 8min

Corrección para SD e IE:

Distancia Lunar_app = 75deg 8min + 15min + 2min = 75deg 25min

Yo también medi la altitud de la Luna y la Capella antes y después de la distancia lunar. Luego interpolé por el tiempo LD.

Ha_moon = 31deg 11.3min

Ho_moon = 31deg 56.4min

Ref = 1.5min, PA = 46.6min

Ha_capella = 19deg 7.5min

Ho_capella = 19deg 4.8min

Ref = 2.7min

Usando la Fórmula Dunthorne, yo inserte el Ha, Ho para la Luna y la Capella y obtuve la Distancia Lunar Geocéntrica en el tiempo de medición.

LD_geo = 75.25597deg

Asume que el tiempo está en algún lugar entre 0700GMT y 0800GMT. Yo calculé el Lunar Distance_geo como la gran distancia del círculo entre MoonGP y CapellaGP en estos dos momentos.

LD_geo@0700hrs = 75.357039deg

LD_geo@0800hrs = 74.90875deg

LD_geo@07xyhrs = 75.25597deg

Usando interpolación lineal el tiempo es:

[(0.101069/.448289)*60min]+07:00:00 = 07:13:31.6sec

El tiempo de medición real fue:

07:13:25

Time Error = 6.6seconds

Introduction

AIS Automatic Identification System for Ships is a traffic system that uses VHF transponders on vessels to periodically send out location information. It was developed by Swedish inventor Hakan Lans and is similar in concept to the ADS-B transponder system used on aircraft for position reporting.

AIS uses two VHF marine channels 87B (161.975 MHz) and 88B (162.025 MHz). Transmission is by 9.6Kbps GMFSK modulation using HDLC packet protocol. VHF channel access is by SOTDMA Self Organized Time Division Multiplexing. AIS uses navigational information from external on board GPS, Inertial Navigation and Ship Control systems. AIS has several different classes of equipment such as Class A, Class B, Base Station and Aids to Navigation. Depending on the Class, different types of information are transmitted when the ship is in port, or underway.

Reception

AIS can be decoded using very simple equipment. An RTL-SDR receiver as described in an earlier post can be used together with a simple vertical whip antenna installed outdoors with line of sight to the shipping of interest. Packet decoding can be done by programs like Multipsk, a popular amateur radio program developed by Patrick Lindecker F6CTE.

References

#1 – “Automatic Identification System”, Wikipedia
https://en.wikipedia.org/wiki/Automatic_identification_system

#2 – “All About AIS”, Created by IMO/IEC Experts
http://www.allaboutais.com/index.php/en/

#3 – “RTL-SDR Receiver”, NooElec-NESDR
https://www.amazon.com/dp/B009U7WZCA

#4 – “MULTIPSK” Digital Mode Decoder by Patrick Lindecker F6CTE
http://f6cte.free.fr/index_anglais.htm

Sunday July 14th was an excellent evening to measure a Lunar. The sky was perfectly clear and the Moon and Jupiter were clearly visible from my apartment balcony. This is generally not the case as there has been so much local construction in recent years.

The distance measured from the Moon_NearLimb to the centre of Jupiter = 16deg 1min

Sextant Index Error = 2min off

MoonHP = 55.7min

Moon Semi Diameter + Augmentation = 15.3min

Lunar Distance_apparent = 16deg 1min + 2min (IE) + 15.3min (SDs) = 16deg 18.3min

MoonGP: GHA = 52deg 40.7min DEC = 21deg 57.6minS

JupiterGP: GHA = 69deg 55.4min DEC = 22deg 10.5minS

Geo Centric Lunar Distance = 15deg 58.5min

Hc_moon = 19deg 54 min (Seen in Toronto)

Az_moon = 153deg 40.2min

Hc_jupiter = 23deg 32.6min (Seen in Toronto)

Az_jupiter = 170deg 25.5min

Ha_moon = Hc_moon + R – PA

Ha_moon = 19deg 54min + 2.7min – 52.6min = 19deg 4.1min

Ha_jupiter = Hc_jupiter + R = 23deg 32.6min + 2.2min = 23deg 34.8min

Lunar Distance_apparent_calculated = 16deg 14min

Lunar Distance_apparent_measured = 16deg 18.3min

Error = 4.3min

Miré hacia el Caribe desde la playa del Condado, imaginé que Ponce de León estaba parado en el mismo lugar, midiendo el ángulo del sol con su astrolabio.

Ponce de León conocía su posición exacta porque le preguntó al Taíno Cacique Agueybaná dónde se encontraban exactamente en la galaxia. Así pudo calcular su intercepción.

Tomé una medida y los parámetros fueron:

El Tiempo = 16 de marzo de 2019 11:53:15GMT

Hs = 18grd 10.5′ ( Miem. Inf.)

Alt de Ojo = 2m

Error de Sextante = +4′

Ha = Hs +/-EdeS – Incl = 18grd 10.5′ + 4′ – 2.5′ = 18grd 12′

Ho = Ha – R + SD = 18grd 12′ – 2.9′ + 16.1′ = 18grd 25.2′

Intercept = Ho – Hc = 18grd 25.2′ – 18grd 23.4′ = 1.8′ = 1.8Nm

Recientemente visité el Castillo San Felipe en San Juan Puerto Rico. Nunca he visto una fortificación tan enorme e impenetrable como esta. Me imaginé que era un soldado español en el siglo XVI y que el pirata Drake apareció alrededor de la Punta Escabron. Tomé el rumbo de la brújula y disparé el cañón, ajustándome al rango.