[HN Gopher] Using NASA's SMAP satellite to detect L-band interfe...
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Using NASA's SMAP satellite to detect L-band interference
Author : c16
Score : 288 points
Date : 2025-05-08 08:52 UTC (14 hours ago)
(HTM) web link (radioandnukes.substack.com)
(TXT) w3m dump (radioandnukes.substack.com)
| o_1 wrote:
| Very awesome. Never knew about L-band.
| 4ad wrote:
| Doesn't really answer the question of _why_ does the military use
| the L-band. Whether it 's jammed or not is immaterial (of course
| they are going to jam it if it has military use), but what
| specific attributes makes L-band useful for the military?
| echoangle wrote:
| If I understand the article correctly, the actually used
| frequencies are close to the L-band but the jamming is
| broadband and also affects the L-band.
| myself248 wrote:
| The L-band is a term for the whole swath between 1 and 2 GHz.
| It's diced into dozens of allocations by international
| treaty.
|
| Some ranges are set aside for GPS/GNSS:
| https://gssc.esa.int/navipedia/index.php?title=GNSS_signal
|
| Some are monitored by the SMAP satellite:
| https://en.wikipedia.org/wiki/Soil_Moisture_Active_Passive
|
| (Also in the L-band are all sorts of other things. A lot of
| cellular bands, known in the US as PCS and AWS, and more.
| Several different sat-phone systems. ADSB in 1090 is juuuust
| inside L-band. And more...)
|
| All transmitters produce a bit of out-of-band interference,
| beyond where they meant to transmit. This is filtered to
| reduce it to a certain level below the intentional frequency,
| but filters aren't perfect. So when someone tries to jam GPS
| or other services, they inevitably bleed some energy into
| neighboring allocations too, some of which seems to be being
| picked up by SMAP.
|
| Note that SMAP's passive radiometer doesn't have pinpoint
| spatial resolution, 36km is stated. This means it's listening
| to a pretty significant patch of ground at any given time, so
| for a source to be picked up among all that, it's got to be
| pretty loud. It also means that attributing the source is
| limited in precision, you can get to city level but not city-
| block level from this data.
| touisteur wrote:
| Yes, civilian radarstuff (Mode S, SSR, ADS-B as you said,
| and other multilateration schemes) use 1090 (downlink and
| broadcast) and 1030 MHz (uplink). Closer to military uses,
| IFF might also use the same frequencies.
| cebert wrote:
| L-band is capable of long range with lower power and can
| penetrate water and foliage. I can see why this could be
| appealing for military purposes.
| bc569a80a344f9c wrote:
| To expand a little bit, RF is subject to free space path loss
| - signal strength decreases proportional to the square of the
| frequency and the square of the distance. The higher the
| frequency, the less far you go. Of course, weaker signals are
| harder to distinguish from noise so there's only so weak your
| signal can go. If you want to control drones, lower
| frequencies are better.
|
| There's a reason that microwaves (the cooking instrument,
| named after the rough band of RF frequencies it uses)
| interfere with WiFi when improperly shielded: they run at
| approximately 2.4GHz. That's a part of the band that's free
| to use without licensing (ISM band, runs at 900MHz, 2.4GHz,
| 5Ghz, and so on). That's because microwave manufacturers
| don't want to license spectrum, and it's the part of the ISM
| band closest to the ideal absorption frequency of water. The
| point of microwaves is to push energy into water molecules
| and make them move around faster, aka heat them. Water
| molecules do that well at 2.4GHz. This also means that water
| blocks RF at that frequency very well, because it absorbs it.
| Trying to shoot 2.4GHz WiFi through trees sucks because it
| gets blocked by the leaves.
|
| So you want to control drones. You can't be around 2.4GHz
| because rain would screw you up. You can't go above that so
| you can get enough distance. You can't go as low as 900MHz or
| other stuff on the ISM band might interfere with you.
|
| Not that much left, given that 1.7GHz is a popular cell phone
| frequency, and so on - you can look at publicly available
| frequency charts to see what's assigned for what where.
|
| This glosses over a lot and is heavily simplified.
| ratatoskrt wrote:
| There is no absorption peak of water at 2.4GHz. Even worse,
| the absorption spectrum will change when it heats up.
| immibis wrote:
| AFAIK the ISM band was placed there because of microwave
| ovens, not the other way around.
| TrackerFF wrote:
| Navigation systems (GNSS) tend to fall right in the L-band. For
| example, the Russian GLONASS is in the 1.2 and 1.6 GHz range,
| while GPS is around 1.1, 1.2, 1.5 GHz.
|
| SMAP is in the 1.2 - 1.4 GHz range - so it overlaps with both
| GLONASS and GPS.
|
| So jamming in that range will affect the nav systems of the
| drones. This is the reason you see drones tethered with fiber
| optic cables - control systems might be in the same range. The
| "why" has more to do that the machines are made to adapt to
| existing systems, and those systems were designed due to the
| physical properties they've made to serve / solve.
|
| Both jamming and spoofing is pretty normal when you're close to
| Russia.
|
| And this is the reason SMAP will pick up all this jamming,
| because it is sensing on the same band / range.
| sandos wrote:
| I mean, in a drone way every frequency is usable. If its not
| that usable, it might still be usable if nobody knows you are
| using it yet, and therefor not jamming it yet.
| nanna wrote:
| Anyone care to explain in layman's terms what this is about?
| echoangle wrote:
| There's a satellite that's measuring ground moisture by looking
| for radiation in a specific frequency. Some jammers in Ukraine
| (devices that send noise on radio to make communications
| impossible for other people) emit radiation in this frequency
| which makes it visible when looking at the data from the
| satellite.
| someothherguyy wrote:
| https://en.wikipedia.org/wiki/Brightness_temperature
|
| https://web.archive.org/web/20230517192717/https://aquarius..
| ..
| echoangle wrote:
| I edited my comment, you're right that the measurement
| isn't really ground temperature.
| egorfine wrote:
| > make communications impossible for other people
|
| for occupying armed forces.
| echoangle wrote:
| Well both sides are jamming, but that's one reason to jam,
| yes.
| pc86 wrote:
| The jamming doesn't discriminate. Domestic armed forces and
| civilians are also impacted, so "other people" makes sense.
| op00to wrote:
| There is a satellite that listens to solar radiation reflected
| off the earth to tell different things like ocean salinity.
| That particular frequency is also used in warfare. This
| satellite can be used to find areas where electronic
| countermeasures are in place.
| mrweasel wrote:
| They used freely available NASA data to map Russian and
| Ukrainian electronic warfare systems. The jammers used leak
| into the 1.4 GHz spectrum, which is suppose to be silent, and
| does so which sufficient power that you can be pretty sure it's
| man made.
|
| So if you're looking for an intersting target, you could do
| worse than those lit up areas.
| parsimo2010 wrote:
| Small correction: the jammers used are specifically targeting
| the L-band, because it is used for navigation and satellite
| communications.
|
| Normally ground transmitters in this band are using just a
| couple watts or less, so they don't significantly impact the
| readings of a satellite looking at a large area on the earth,
| but a jammer uses a lot more power and can be noticed.
| toomuchtodo wrote:
| _US to Provide Anti-GPS Jammer Sensors for Ukraine's
| Precision-Guided Bombs_ - https://www.kyivpost.com/post/32163
| - May 6, 2024
| x0 wrote:
| Brilliant idea to check out this satellite. Are there any others
| that receive interesting frequencies? (thinking under 6GHz)
| NitpickLawyer wrote:
| People have been tracking the actual "true" front lines since
| the war began with that IR "fire early warning" satellite from
| NASA. Turns out a satellite that's good at detecting natural
| fires is also good at detecting explosions / fires started by
| explosions.
| TechDebtDevin wrote:
| Another interesting tracking mechanism was the use of Apples
| Wifi Positioning database, which allowed researchers to track
| front lines via Starlink wifi access points.
|
| https://www.youtube.com/watch?v=hlbjUvkoyBA
| Scoundreller wrote:
| gonna spoof my AP to use a Starlink MAC, brb
| folli wrote:
| Do you have any links further elaborating this?
| bob1029 wrote:
| Iridium satellites can communicate with ground stations on
| L-band.
|
| This band is extremely useful if you're stuck on a ship in the
| middle of a typhoon and need to get some help.
| qwertox wrote:
| How does this work? Do they just listen and never transmit,
| unless they receive a targeted emergency message?
| os2warpman wrote:
| L-band is used for voice and data communications to handheld
| devices by several satcom providers.
|
| At a very high level handheld satellite communications
| devices work just like regular cellphones, except they also
| function in the middle of the ocean.
| russb wrote:
| L-band signals can penetrate through clouds and rain. This
| property is why L-band is used for GPS and other applications
| that require all-weather operation, as it allows for accurate
| data collection even in the presence of adverse weather.
| mellow_observer wrote:
| What do the jamming locations within Russia correspond to? You
| would think these are important places that require drone
| protection, but I could not quickly discover what is so important
| in these places.
|
| For instance, the bright spot to the north west of Moscow seems
| to fall somewhere in or close to Zavidovo National Park. Is there
| something important there? There's nearby air bases Migalovo and
| Klin, but both seem too far from the center.
| TrackerFF wrote:
| Russians will place out jammers close to anything of
| importance. For example, in the Kola peninsula - which is close
| / bordering both Norway and Finland, they're jamming and
| spoofing. To such a degree that it affects civil air traffic in
| the area.
|
| But why? Because they have a bunch of major strategic airfields
| there.
|
| In (and close) to Ukraine it could be anything. Airfields,
| base, ammo storage, radio towers, etc.
| nicce wrote:
| Hmm, do they really jam 24/7 in the Kola peninsula? I thought
| that mostly happens when there is some sort of military
| exercise.
| TrackerFF wrote:
| Before 2022 they'd mostly conduct jamming operations as
| part of their military exercises, but after they've started
| jamming and spoofing much more - as a security measure
| against drone operations. Ukrainian drone operations have
| taken place as long north as Murmansk, which is roughly 90
| miles / 145 km from the closest Norwegian airport
| (Kirkenes).
|
| EDIT: 5 days ago they shot down Ukrainian drones there
|
| https://www.thebarentsobserver.com/security/russian-war-
| mini...
| nicce wrote:
| Oh yeah, that explains the shift.
| cenamus wrote:
| Do we know how effective GPS jamming is against the
| military bands? (Ukraine probably doesn't have access to
| those but still)
| mandevil wrote:
| Both military and civil GPS signals are L-band. Any
| jamming that runs across the L-band will hit both of
| them. And since the frequencies are publicly available
| (and it is possible to confirm that they are correct with
| your own detecting equipment) it is not any harder to jam
| the purely military frequency versus the civil and
| military frequency. The only thing is having more
| frequencies to jam should mean less power on any given
| frequency for a given amount of power, especially since
| you would probably want to jam BeiDou and Galileo signals
| as well (all also on the L-band). I mean, since Ukraine
| and Russia can buy things on the open market, they could
| buy BeiDou receivers just like GPS, so I would expect
| them to target all of those frequencies.
|
| Block III GPS satellites added a new feature, designed to
| help the military signals defeat jamming. They added a
| "spot beam" - a high gain directional antenna capable of
| covering an area about 200km wide with 20db extra power,
| to try and burn through jamming. This spot beam is only
| used for military signals, and it requires extra
| processing on the receiver to use (since the satellite
| still has the earth-wide antenna broadcasting the
| military signals, a military receiver inside the spot-
| beam area would see two different signals from the same
| satellite, absent jamming).
|
| During the Biden administration, at least, USAF ISR
| assets spent a lot of time running race-tracks just at
| the edge of Ukrainian airspace, monitoring events in the
| country, and I would expect that would be something that
| would be a good use case for the spot beams, though I
| don't know about Ukraine ever getting any of those
| receivers, and I would not expect coordination with the
| USSF on pointing the high gain antenna to support UAF
| operations even under Biden, but all of that is my
| speculation, I haven't seen anything on where these high
| gains are pointing.
| bobmcnamara wrote:
| Heck, they used to jam some frequencies 24/7 worldwide!
| nicce wrote:
| I think that prior 2022 they still had to consider the
| political impact, at least on some level.
| bobmcnamara wrote:
| They shut down the western steel work radar because of
| power cost increases after Chernobyl blew, combined with
| the improved value provided by surveillance satellites.
| toomuchtodo wrote:
| _GPSJam: Daily Maps of GPS Interference_ -
| https://news.ycombinator.com/item?id=32245346 - July 2022
|
| https://gpsjam.org/
| Bengalilol wrote:
| Thanks!
|
| The amount of locations with GPS jam is impressive (compare
| march 2022 and may 2025).
| toomuchtodo wrote:
| GPS jam uses data from aircraft ads-b GPS accuracy data
| reported, so they should have global air traffic route
| coverage. Would be interesting to fuse that data with this
| data (sensor fusion).
| dylan604 wrote:
| Is that the forest where the politburo members have the dachas?
| g4zj wrote:
| Wouldn't NASA then almost certainly be aware of this as well?
| parsimo2010 wrote:
| This satellite's mission is soil readings. Most scientists are
| not part of the intelligence community. They may have noticed
| anomalous readings and excluded them from their analysis, but
| they don't really have anyone to talk to about the military
| implications. Plus, while this is cool that you can detect this
| interference with a science satellite, the major space powers
| all have military and intelligence satellites that can map the
| interference at greater precision, so the NASA scientists can
| pretty much ignore this unless they are particularly interested
| in the soil readings in this part of the world.
| g4zj wrote:
| Thank you for that explanation. It was very helpful. :)
| frandroid wrote:
| It's not impossible that the Pentagon could have thought
| "alright, we want these readings. is there a civilian use for
| this kind of data and decided to see if a civilian project
| could be sprung up... Though that's more of a Cold War
| conceit. These days they would just do it themselves, it's
| probably an easy and cheap project.
| robocat wrote:
| Just as there are commercial earth imagery satellites, I
| would expect there are commercial RF source detection
| satellites. There are obvious sales channels to hedge
| funds, countries, militaries, and commercial transmission
| operators (searching for causes of interference).
|
| Hedge funds is the fun one: detecting economic activity and
| growth (independent of official government figures).
| dakr wrote:
| I don't think this is lost on anybody, even if it's not the
| main mission. SMAP also provides a near-real-time data product
| which may interest people in this area.
| NoSalt wrote:
| His GitHub site mentions: _" This script processes NASA SMAP L1B
| .h5 data files"_, but he doesn't say how he obtains these data
| files. Is he using an API, or is he using something like an RTL-
| SDR to pull the data directly?
| williamscales wrote:
| Looks like they're available here:
| https://nsidc.org/data/smap/data
|
| And there's some info here: https://smap.jpl.nasa.gov/data/
|
| Very cool stuff!
| sstanie wrote:
| You can search on ASF's data discovery portal for SMAP:
|
| https://search.asf.alaska.edu/#/?maxResults=250&dataset=SMAP...
|
| This lets you bulk download the .h5 files once you have an
| Earthdata account (https://urs.earthdata.nasa.gov/home )
|
| or you can use the libraries if you'd like,
| https://github.com/nsidc/earthaccess or
| https://github.com/asfadmin/Discovery-asf_search
| logicziller wrote:
| This is brilliant. What other bands can we observe like this?
| lokimedes wrote:
| SAR satellites have also prove useful:
| https://medium.com/@HarelDan/x-marks-the-spot-579cdb1f534b
|
| Sentinel 1, if I recall, is C band. But the technique would
| work for X-band as well, like TerraSAR-X and other commercial
| satellites.
| Alex-Programs wrote:
| ```In a modern conflict zone, jamming L-band means blinding
| drones, degrading targeting, and cutting off ISR. It's not
| accidental. It's deliberate.
|
| The international treaties that say "don't transmit here"? Those
| don't matter much when you're trying to survive a drone swarm.```
|
| LLM prose, and it's not the only section that stands out. It's an
| informative article, so I don't mind it as much, but I think it's
| a shame people don't write things themselves anymore.
| piskov wrote:
| What exactly stands out? Besides the fact the author is most
| likely of ex-USSR descent, i. e. not a native speaker.
| philsnow wrote:
| This doesn't read like LLM spam to me. Punchy 2- and 3-word
| sentences are a rhetorical device that I haven't seen ChatGPT
| (at least; I haven't really used the others) use at all.
| dakr wrote:
| A wonderful example of the useful, sometimes unintentional
| secondary effects of doing science. SMAP as a mission is firmly
| in the Earth science category, so very much in the crosshairs of
| the current administration. The data is used for Earth science
| and climate research and has many agricultural and water
| management applications.
|
| For example, water management districts can tell if the local
| soil can accommodate the water from an upcoming storm or if the
| water will stay on the surface and cause flooding.
| jjwiseman wrote:
| I liked this overview map they posted a few days ago:
| https://x.com/HamWa07/status/1919763145536463222
|
| giammaiot2 on twitter has a long history of trying to use science
| sensors to detect intentional RF interference, e.g. this post
| with a map from the Advanced Microwave Scanning Radiometer (AMSR)
| looking at 7 GHz:
| https://x.com/giammaiot2/status/1919493425100988490
|
| Or this thread from 2023 looking at SMAP:
| https://x.com/giammaiot2/status/1770815247772729539
| anthomtb wrote:
| Thank you, that map is fascinating. Jamming in and around
| conflict zones (Ukraine, Myanmar) and in China make sense to my
| Western brain. But why so much interference in Japan?
| drmpeg wrote:
| The specific allocation is 1400 to 1427 MHz. It is reserved for
| radio astronomy (the hydrogen line is at 1420.4 MHz), passive
| (receive only) Earth exploration satellites and passive space
| research.
|
| In the US, 1240 to 1400 MHz is allocated to radar. GNSS downlinks
| at 1240 to 1300 MHZ are not protected in the US.
| kevin_thibedeau wrote:
| Crimea is still part of Ukraine. That can't change until a peace
| treaty settles the dispute.
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