that there's a lot of silt down there. that could complicate the search because the silt on the bottom of the ocean can be very thick and things disappear in to it and it makes a visual search underwater very difficult. >> on monday, you thought there was possibly two pingers. to you think you are dealing with two or one device at this point? >> well, we have the evidence. the assessment was made that we thought there might be two pingers there. this has not been confirmed in further detections that we picked up. now, whether that's because, you know one ping er has run out of battery life and there's one running, or we just haven't got close to it, i don't know. but the fact of the matter is we haven't had any further evidence of two pingers going off in the