I agree that ELINT is a double-edged sword. But if the chinese ELINT just passively collects US signals, how would the US ever collect chinese signals?
ELINT is not merely passive. You can have a 'provocation' transmission. You can make physical 'incursion' or approaches territorial boundaries and collect electronic responses. It does not matter if the target is at land or floating at sea. Even the lack of any electronic responses can imply certain capabilities and/or intentions. But all crafts, air or seaborne, wants to be alerted of approaching objects and to date, radar remains the best detector mechanism. So collecting the sweep patterns and freqs of this ship can tell US a lot of its capabilities. Photos of the ship's antennas and their locations on the ship's structures can tell US its collection capabilities.
The US is a highly industrialized country, arguably the most in the world, and that mean the US military have a lot of electronic cover, junks like radio and television transmissions, that we can use to mask our 'provocation' transmissions and collect the ship's responses. Or none at all. We can use over-the-horizon radar transmissions as one such 'provocation' transmission and have a sub record this ship's electronic responses when it detect those radar transmissions. The one very important item is receiver sensitivity. The less sensitive the hardware, the shorter in distance between the two players when there are responses, and that is very telling of one side's technology level.
Diffraction loss =>
Diffraction <= Is extremely important in tactical ELINT for both sides. Geographical features are always open for exploitations to gain advantages in combat, so knowing how to lure an adversary into an electronically disadvantageous position due to terrain is valuable knowledge. Beside receiver sensitivity, other important hardware related items are freq and bearing azimuth coverage, beamwidth and
INSTANTANEOUS bandwidth. If a potential war adversary is capable of frequency agility, there is a crucial need to have wide bandwidth capability, in transmit and receive, and to have that capability as rapid as possible, to collect his transmissions, else you would lose the freqs he is capable of moving into.
The US is a consumate pro in EW at all levels, from the SR-71's missions over Soviet territory to ground collectors. I used to ruck about 100 kg of electronic junk to collect an airbase's electronic data recorded on magnetic tapes. We trained ROK Marines on signal exploitations. We buried ourselves in the snow outside of Osan and Kunsan airbases and collect electronic emissions, from radars to handheld radios, called 'bricks', used by maintenance to keep the aircrafts flying. No one eat and we had what the kids called 'energy drinks' today. We pissed in ourselves and make sure the liquid is covered by our bodies to deny the defenders any IR signatures. Generators are emitters. So do jet engines. All are unique. At such close proximity, it is possible to create a very accurate combat capability profile of an airbase f.rom ELINT. I advise you temper your enthusiasm upon considering this potential war adversary.
Plus, ELINT is not a form of direct confrontation, the US can't say any thing about it since they do intelligence gathering the South China Sea all the time.
We do not want to have any kind of 'confrontation' as long as this ship remain outside territorial waters. But we do encourage the PLAN to send it our way for US to scope it over.