There are a few ways you might get feedback from the kite, without using vision.
1) GPS. Don't rule this out simply because the kite's base might be in a different location each time you use it. To counter this, you simply need a GPS receiver on both the kite and the base. Take both readings, and convert them into Cartesian coordinates. The difference between these coordinates is the offset of the kite from the base. Note that while GPS offers fairly low accuracy, its resolution is better than its accuracy. The kite and the base will both have the same position error, and so the kite's location relative to the base can be (reasonably) accurately calculated.
2) IMU. A 9-axis Inertial Measurement Unit, will help. There are some pretty small, lightweight parts available, like the MPU-9150 from Invensense. If you use a Kalman Filter to combine the GPS reading with the IMU reading, you can hugely increase your position resolution.
(Sorry, that's a similar part, but the same size)
3) Load cells. The reason I asked how easily you could fly a kite with your eyes shut, is because this will give you some idea of how useful the information from Load Cells will be. Perhaps you wouldn't be able to fly the kite brilliantly, but I bet you could keep it in the air. Each kite string will need a 3-axis force measurement so that you know the exact force and angle of each string. Arrange the three load cells like this:
Each one has a string coming perpendicularly out of the top, in the direction of the load cell's maximum sensitivity. Tie the three strings together, and to the main kite string. The sum of the three measured force vectors will be the tension and direction of that kite string. Make sure that the angle between the strings is greater than the maximum angle of the kite string, otherwise one of the three strings may go slack, making for a false measurement.
4) Pressure. I'm sure you could learn a lot by measuring the air pressure at several points on the kite's inside surface. There are some tiny lightweight barometric sensors available, like the BMP085.
It's even available from Sparkfun on a breakout board. These sensors will also help you to measure the kite's altitude (if they're out of the wind), and you can even use them to measure the windspeed if you place two inside a pitot tube.
Four sensors and three Pitot tubes, plus one sensor on the ground, will give you wind speed and direction, and altitude.
Best Answer
There are a few commercial devices to find lost remotes, keys, and other small items. They usually work by having a small radio frequency (RF) receiver that uses a button cell and attaches to the item intended to be found. (It's similar to a keyless entry fob for your vehicle.)
When the item goes missing, the user presses a button on a base station (or sometimes another remote-size thing; which I suppose could also get lost, but that's another subject...). When the receiver picks up the signal, it emits a beep and/or flashes a light, etc.
Bluetooth is only designed for about 10 meter (30 ft) range, but higher power Bluetooth devices could have ranges up to 100 meters (300 ft).
Some commercial products that are similar to your need:
And a discussion about a device that might respond to sound instead of RF: