@ heat detection is the most commonly mentioned method. Infrared cameras look for hot spots that could be cave entrances or vents. Some of the more elaborate caves have baffles and other systems to reduce heat signatures, and some caves are so deep that any heat inside them has long since cooled as it passes through a mile or more of tunnel to the surface.
@ Seismic detection can only be done from the ground. After deploying a series of listening posts, sound is transmitted in the ground using an explosive device or a large hammer. The resulting echoes can be charted and can find tunnels better than any other system, but there are relatively few experts who can read the data and actually say "there is a cave here".
@ Earth resistance tomography. Electrodes are deployed and a current is run through the ground to map the electrical resistance. UN inspectors have used this in Iraq. Teams in the US have detected tunnels up to 45 feet deep. This can be done from aircraft, but only if they fly very low. This is dangerous in Afghanistan due to enemy weapons and the rough terrain.
@ Ground-penetrating radar can be used from aircraft or the ground. Low-power sets are used by many cities to locate utility tunnels up to 20 feet down. More powerful sets are used by the military for detecting caves and tunnels. Aircraft can cover wider areas but with a lower chance of detecting something.
@ Passive listening can, given luck, time, and a big computer, detect human voices or other human activities. Due to the vagaries of natural rock, however, this technique is fairly hit and miss. It works in Korea where any tunnels would obviously be in the DMZ, but to search wide areas it is not particularly effective. It can be used to investigate caves discovered by other methods.
@ Micro changes in gravity can be detected by special instruments. The gravity over a cave might be only 99.9999% of the gravity over nearby rock. This is a time-consuming technique but can be useful in some cases. NASA uses similar technology from the space shuttle, but that would not be sufficiently precise to locate individual tunnels.
@ Geological signs of caves can sometimes be seen from satellites or aircraft photos, but given the jumbled Afghan terrain this technique is not particularly effective there. The French Mirage-IVP recon plane used in Afghanistan flies at treetop level in valleys, taking horizontal photos of cliff faces to look for cave entrances invisible from directly above.
@ An old cave hunter technique is to find a mountain stream that disappears into a cave and pour harmless dye into it. The appearance of the dye in a nearby valley will often reveal the extent of the cave system. Conversely, cave hunters will put smoke into a lower cave entrance and wait to see it appear in natural vents on the hillside above.
@ The most effective method of finding a cave, however, is to talk to someone who already knows where it is. US teams are interviewing thousands of villagers, warriors, and prisoners to ask them about known cave complexes in their areas.--Stephen V Cole
Some 4,000 troops from America, France and Italy are moving into Kulyab airbase in Tajikistan. Some 50 warplanes, mostly American, are also arriving.
The fighting in the Tora Bora is slow. The Taliban have the high ground and many caves and the area is heavily forested. When American troops first encountered this sort of thing in the Philippines 56 years ago, they used artillery and tanks firing directly at the caves, and fighter-bombers coming in low to drop napalm. It worked, but it was slow and dangerous. After the war, an attempt was made to build a surface-to-surface missile that could be precisely guided into the mouth of a cave. This system, the Lacrosse, cost a lot of money in the 1950s and never quite worked as intended. But it demonstrated the concern World War II veterans had about a future war featuring enemy troops in caves. The precision glide bombs used in Afghanistan can finally do what Lacrosse could not. Around Tora Bora, whenever Afghan troops encounter al Qaeda defenders, they pull back a bit and American special forces troopers send in a 2,000 pound bomb, or a smaller cluster bomb (that catches any al Qaeda in the open.) Journalists coming up the hills behind Afghan troops see the unmistakable evidence of smashed al Qaeda positions. Sometimes the Afghan troops can advance so fast that the surviving (and retreating) al Qaeda were forced to abandon supplies of ammunition. After the bomb attacks, al Qaeda troops can be heard making desperate calls to units that just disappeared in a bomb attack, or from survivors of such attacks, with fear and panic in their voices, asking for medical help or instructions on what to do next now that Afghan troops were closing in. As a result of these tactics, al Qaeda forces have lost most of the rugged terrain around the main Tora Bora cave complex, and taken heavy casualties in the process.
Most of the Afghans fighting around Tora Bora have only light weapons (assault rifles, machine-guns, mortars and portable rocket launchers), plus four tanks. There are about a hundred U.S. troops involved in the Tora Bora fighting. In addition to the bombers, there are also some attack helicopters seen in the area.
One of the Afghan commanders fighting al Qaeda troops at Tora Bora announced a ceasefire because the al Qaeda troops he faced had asked for surrender negotiations. The al Qaeda were given 24 hours to surrender, but there is concern that negotiations might allow some or all of the al Qaeda fighters to go free. Still no sign of bin Laden or any senior Taliban or al Qaeda leaders.
Two more senior Taliban officials were captured by Northern Alliance forces. Not many Taliban or terrorist (al Qaeda) leaders have been caught so far. The Talban brass, being Afghans, have an easier time getting lost within Afghanistan. But the al Qaeda leaders are mostly foreigners and stand out. While you can flee to some remote village, eventually the word gets out that there are "strangers up there." Taliban or al Qaeda leaders may have large sums of money with them (and gunmen to protect it). This would enable them to buy cooperation in getting out of the country. Smugglers are open to these deals. But the only country that provides any sanctuary are parts of northern Pakistan where there are still a lot of pro-Taliban activity. But the Pakistani government is cracking down on Taliban operations in Pakistan. Again, the money could buy escape by boat or air. But the U.S. fleet is patrolling the Pakistani coast and American reconnaissance aircraft are carefully watching Pakistani air space. The three most likely destinations of Taliban and al Qaeda leaders (Somalia, Iraq and Indonesia) are also being watched. Bin Laden, in particular, has to be careful how he travels. He has a $25 million price on his head. If he doesn't move with a lot (dozens, at least) of bodyguards, he risks being seized by someone eager to collect the reward. But traveling with the bodyguards makes him easier to spot from the air, or on the ground. A few dozen armed followers moving through rural Afghanistan will attract attention.
Over the past three days, Pakistani troops have arrested twenty foreigners trying to sneak across from Afghanistan. Five of the men, most of whom are Arabs, were already wounded. The men had apparently fled south after the fall of Kandahar. Going south makes sense, as this takes them to the coast where, if they have money, they can buy passage across the Indian ocean to Arabia.
Tunnel Hunting Technology- Finding tunnels in Afghanistan is not easy. Entire mountain ranges of limestone are riddled with natural caves, caverns, and tunnels, and these have been improved over a period of centuries. Even worse, agricultural irrigation in the region is done by covered trenches with a well every few hundred feet. These are called "karez" in Afghanistan and "kanat" in Iran. Some of these covered trenches are centuries old and they are a traditional hiding place and movement system. Many techniques can be done by aircraft, but others are done on the ground by special forces and other units. The ground-based systems are more effective, but take much longer and are vulnerable to ambush. Systems and techniques can be used in combination; data from one source might redirect the efforts of another system. A possible tunnel location found by one method might be checked against data on file from other systems. Some methods of detection include: