Doesn't Brahmos is considered to have quite a high bit of maneuverability and terrain hugging/sea skimming capability for a super-sonic missile?
I'm not that knowledgeable on these things, just saying that from what I have heard in some past interviews of ex-DRDO folks.
Sea skimming over sea & over land is completely different thing..... ocean surface is relatively flat & predictable,.... allowing Brahmos radar altimeter & navigation system to maintain a constant altitude of 5 to 10 meters without risk of sudden terrain change.
Over land however terrain changes are abrupt, irregular & highly variable...... mountains, hills, valleys, buildings, tree lines, ridges, etc etc....... At Mach 3 brahmos covers one kilometer every 1 second..... meaning it has almost no reaction time to detect, process & maneuver around obstacles...... Terrain following over land requires, High resolution terrain contour matching sensors (TERCOM), Real time EO/IR terrain readers, High agility control surfaces, Lower flight speed to allow maneuvering.
BrahMos land attack variant does have TERCOM/DSMAC for mid course navigation & accurate position updates..... But it's not a real time obstacle avoidance tool & rely on pre- loaded terrain maps & image correlation, not instant detection of unexpected elevation or terrain changes.......... At Mach 3 even with TERCOM/DSMAC Brahmos has no time or maneuvering margin to avoid sudden terrain features & its control surfaces cannot generate high G turns needed for true terrain following at such high speeds........ Attempting ultra-low-altitude land flight would exceed its aerodynamic & guidance limits & risk terrain impact...... Reason why Brahmos land attack profile includes flying higher until the terminal dive........ which make it more susceptible for interception against a well defended enemy with a good Air defence system..... whereas over the sea, smooth & predictable surface conditions allow very low sea skimming even at Mach 3.
Now let's talk about its seeker...... It uses ARH based seeker & new phased array monopulse seeker which have limitations, it has no other option by the way because of its inherent design......... Active radar is excellent for detecting large metallic targets like ships but is less effective at identifying small, camouflaged or clutter masked land targets especially in environments with heavy electronic countermeasures or decoys....... Modern Subsonic VLO cruise missiles can integrate EO/IR, IIR, multispectral sensors & Automatic Target Recognition algorithms, which provide much higher target discrimination & can visually confirm or classify the target in real time....... This means missiles like JASSM ER, Storm Shadow can strike hardened relocatable or time sensitive land targets with greater autonomy & lower chances of misidentification.
Radar seekers are inherently more susceptible to jamming, deception & clutter spoofing......... whereas passive IR/IIR, high fidelity electro optical/TV seekers are immune to RF jamming & offer far better discrimination in difficult environments...... Brahmos inability to use passive optical seekers due to heating, shock, plasma interference & extremely short observation windows at Mach 3 reduces its effectiveness in deep strike, stealthy & complex terrain missions...... It's seeker is good for say speed driven naval strike roles but inferior for land attack precision, target classification, anti jamming resilience & multi sensor fusion, all of which subsonic stealthy cruise missiles can achieve far better with their more diverse seeker suites.