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1. Two Radiosonde Recoveries in San Francisco

   The prevailing winds here in California blow from west to east, from the Pacific Ocean towards the Sierra Nevada mountains. Radiosondes launched from Oakland International Airport float in these winds, landing east of Oakland in the Central Valley, or south in the hills east of San Jose. I never recover the ones that land in the Central Valley, as driving 2 hours each direction during rush hour to recover a balloon is a bit too far for me. Only rarely do they land in populated areas in the Bay Area, and almost never on the Peninsula or in the city of San Francisco.

   This map (code below) shows the landing locations of all the radiosondes launched from Oakland since November 2020, when I started receiving them. Each red dot is the last position received by my two receiving stations, and is typically less than 1,000 meters altitude. This map shows 337 radiosondes, and I have removed the radiosondes launched up north by UCSD during atmospheric river events. As you can see, they are mostly south and east of the ...

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2. Telemetry from an Oakland Radiosonde Floater

   In the beginning of March, something happened to the regular cadence of radiosonde launches from Oakland Airport. No balloon was launched on March 11th 2300 UTC, nor the next standard launch window on March 12th 1100 UTC (5am Pacific time). The SDM Ops Status Messages had a 10142 error for Oakland, which is ground equipment failure. I'm guessing that something broke or got jammed on their autolauncher, or maybe they ran out of hydrogen gas.

   By the afternoon of March 12th, the issue appeared to be resolved, and there was three launches in quick succession. The first and third balloons, S3231708 and S2321334, were normal, but the middle balloon slowly rose and leveled out around 35,000 meters (~115,000 feet), and became a "floater" radiosonde. Maybe was underfilled with hydrogen gas, or had a hydrogen/air mixture instead of pure hydrogen.

   The serial number of this floater balloon was S3240385, and it launched around 20:40 UTC on March 12th.

   

   Due to buildings in the way, I stopped receiving the balloon west of Santa Cruz, and started picking it ...

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3. An Atmospheric River of Radiosondes

   I recently installed a new antenna (see below), and checking SondeHub a few hours later I noticed a bunch of balloons west of Sacramento. Well, that's pretty interesting. There aren't any regular launches near Sacramento, so this must be something special. They seemed to be launched frequently, because when I stopped receiving one balloon I immediately start receiving the next.

   

   These balloons were far away! I guess this new antenna works a lot better than the old one. Trying to back out the launch location, it seemed like they were being launched from Beale AFB, which is directly east of Yuba City. Maybe a military project? The military does launch a lot of radiosondes, but those are usually in Arizona in support of Aerostats patrolling the border.

   The program I use to decode radiosondes, radiosonde_auto_rx, supports multiple receivers, so I stole a RTL-SDR from my AIS station and continued receiving. The next day I saw radiosondes above Santa Rosa as well.

   

   Where were all these coming from? Using the telemetry I was directly receiving from the balloons, and the low-level ...

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4. Two Months of Radiosonde Balloon Reception

   It's been two months since my first radiosonde recovery. In this post, I perform some analysis of the receiving stations at my apartment in San Francisco and my vacation home/parents place in Los Gatos. I also include the python code needed to generate your own plots.

   San Francisco Station

   Immediately after I got home from my first recovery, I converted my regular amateur radio station at my apartment to receive radiosondes. The external antenna is a Diamond X-50NA, which is a great amateur radio 5/8 wave 2m/70cm dual-band antenna. Coax up to the roof is about 80 ft of LMR-400, which is calculated at around 1.5 dB loss at 145 MHz and 2.5 dB at 450 MHz, plus connectors. Because this had a base station radio attached, it didn't have an LNA or filter up at the antenna.

   Here is a pic of the antenna, mounted to a 5 ft pole that is clamped to a steel sewage roof vent. This is a very easy (temporary) installation. The Nanostation M5 also installed is part of ...

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5. Two Radiosonde Payload Recoveries, and RS-41SGP Teardown

   I've been watching SondeHub for the past two months to, every day since my first recovery, but the winds have not been cooperating! Lots of radiosondes went into the hills east of San Jose, out into the ocean, into the Santa Cruz mountains, all the way down to Gilroy, or splashed down in the bay, but none have landed in populated areas within an hours drive of my home in San Francisco. I realized how lucky I was that the first radiosonde I successfully tracked actually landed in a populated place.

   In a typical city, approximately 35-50% of the land is dedicated to cars: residential roads, arterials, freeways, and parking lots. So when a balloon lands in populated areas of the Bay Area, there's a really good chance that it's going to land on or near some car infrastructure. Even my neighborhood in San Francisco, one of the densest cities in America, dedicates 28% of surface area to cars: from the center stripe to the front of the house is 40 ft, and the lot is 100 ft deep. Cars ...

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6. Oakland Radiosonde Investigation, Launch, and Recovery

   I've recently stumbled upon the radiosonde_auto_rx project. I've always been interested in tracking radiosondes, and even watched a radiosonde launch in Inuvik, NWT a few years back. Worldwide, there are over 800 launches every twelve hours of every day, and this data feeds into weather forecast models.

   The radiosonde_auto_rx project is built around decoding many different types of radiosondes with a software-defined receiver. The preferred receiver is a RTL-SDR Blog v3, and I already had an extra one of those (because they are so inexpensive!).

   Most radiosondes worldwide use 400-406 MHz as their downlink, but the United States also uses some frequencies around 1680 MHz. Reading the documentation on which frequencies are in use, it appeared that 1680 MHz was being used at Oakland, but they were transitioning over to 400 MHz "sometime in 2020." So first step was to install the software, then find what frequency band the radiosondes were on.

   Software Install

   The radiosonde_auto_rx program is designed for Raspbian/Debian systems. I use a crappy laptop with Ubuntu for my APRS balloon tracking, so I decided to use ...

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7. High-Altitude Balloon Launch from Davis

   The SF-HAB group got together in the beginning of August to do another high-altitude balloon launch. The purpose was to test out a new 3D GoPro camera to see how well it would perform at altitude. We also had a LoRA transciever onboard, which we are thinking about using as a remote cutdown device that we would fly on future launches.

   The jet stream in July was really unsettled, so we delayed for a few weeks while the winds picked up a bit and shifted heading. Watching the predictions from HABHUB gave us a good idea when to launch. This was one of our predictions before launch.

   

   Unfortunately, I really goofed up when doing the launch predictions. As you can see in the above screenshot, I used the default ascent rate of 3.5 m/s, which is about 680 ft/min. We normally target 1000 ft/min, so this prediction has the balloon going much further than what we were looking for.

   I realized my mistake and ran some more predictions, plus the winds changed slightly overnight, so we ...

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8. High-Altitude Balloon Launch from the Berkeley Marina

   After the success of the KD4STH launch in September, we decided to do it again! A new group formed for San Francisco High Altitude Balloons (SF-HAB), and we started scheming. The hardware and time stars finally aligned on Sunday March 8th, and we decided to launch from the Berkeley Marina. Unbeknownst to us, this was only a few days before the whole world shut down due to COVID-19. Great timing!

   

   

   The balloon was a Kaymont 3kg balloon, and we used an entire K-sized tank of hydrogen for lift. Unlike some previous launches, we didn't use weights to carefully measure/specify the ascent rate, we just used the whole tank. During the chase, we calculated our ascent rate at about 1400 ft/min, which was faster than our target of 1000 ft/min. Faster ascent means the balloon is not being pushed around by the wind as much, but it will burst at a lower altitude if the balloon is overfilled. Since this was a 3kg balloon, it was not overfilled.

   

   The primary mission of this launch was to fly a ...

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9. Radiosonde Launch from Inuvik, NWT

   In September 2016 I visited the Environment Canada Weather Station in Inuvik, NWT. I arrived just as they were preparing for the 2300z weather balloon launch, and they let me hang around and take some pictures.

   Every twelve hours around the globe, approximatley 800 radiosondes are launched. These weather balloons record temperature, pressure, humidity, and location from the surface all the way up to 100k feet, or higher. These measurement are fed into weather models for long-term weather forecasting. These launches happen worldwide at 1100 and 2300 UTC, which gives the balloon enough time to be up at altitude around noon and midnight UTC.

   This is the Vaisala RS92-SGPD radiosonde, which measures location, pressure, temperature, and humidity as the balloon ascends. The helix antenna in the upper right is for GPS, and the silver strip below that has two temp sensors and a humidity sensor. The 402.7 MHz wire antenna is on the bottom of the unit, on the left side. The 200 ft of string on the spool attaches to the balloon.

   

   The balloon is filled with locally-generated ...

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