NMAC AND PROX TO GND BY A C152 WHO WAS ATTEMPTING TO OBTAIN THE N-NUMBER OF A HELI THAT WAS TAKING PHOTOS OF HOMES BELOW TPA AND TO THE W OF 2O3; CA.

Narrative

I WAS WORKING CLOSE TO THE ANGWIN ARPT; CA. THE FIELD ELEVATION THERE IS 1848 FT. THE ARPT IS MORE OR LESS THE HIGHEST POINT IN THE VICINITY SINCE THE ARPT IS LOCATED ON A SMALL PLATEAU. WE WERE DOING PHOTO WORK IN THAT AREA. OUR JOB IS TO SHOOT PICTURES OF HOMES. I AM THE PLT AND I HAD A PHOTOGRAPHER ON BOARD. WE WERE FLYING ALREADY WITH THE L DOOR OFF TO ALLOW THE PHOTOGRAPHER TO DO HIS WORK. THAT CAUSED ALSO A LOT OF NOISE IN THE COCKPIT. WE STARTED WORKING OVER THE TOWN OF ST HELENA AT ABOUT XA30. WE WORKED OUR WAY TOWARDS THE ANGWIN ARPT AT ABOUT 1 HR LATER. WHEN I ARRIVED CLOSE TO THE ARPT; I ANNOUNCED ON THE CTAF THAT WE WOULD WORK IN THE AREA; WENT OFF THE ARPT. THE ARPT HAS A PUBLISHED TFC PATTERN WHICH IS R TFC FOR RWY 34 AND STANDARD FOR RWY 16. THE PATTERN ALT IS DEPICTED WITH 2698 FT MSL. SO THE PATTERNS ARE E OF THE ARPT FOR NOISE ABATEMENT. I WAS WORKING W OVER A 'NOISE SENSITIVE AREA.' WHEN I ANNOUNCED MY INTENTIONS ON THE CTAF; I DID NOT SEE OR HEAR ANYBODY IN THE PATTERN OR ON FREQ. DOING PHOTO WORK MEANS FOR ME; FLYING RELATIVELY LOW AND SLOW; BUT STAYING ALSO OUT OF THE SHADED AREAS OF THE HT/VELOCITY DIAGRAM -- WHICH I DID ALL THE TIME. WE WERE ALREADY WORKING ABOUT FOR 1 HR IN THAT AREA; AND I HEARD IN THE MEANTIME GUYS TALKING ON THE RADIO AND SAW THEM ALSO IN THE TFC PATTERN. THEY WERE ALSO CHATTERING ON THE RADIO; BUT I DIDN'T PAY TOO MUCH ATTN TO THEM SINCE THEY WERE ON THE OTHER SIDE OF THE ARPT AND I WAS WORKING BELOW THEIR TPA ANYWAY. WE WERE SHOOTING PICTURES OF HOMES WHICH WERE BUILT ON A STEEP SLOPE; WHEN I DISCOVERED THAT A C152 CIRCLED AROUND US IN A VERY UNUSUAL LOW ALT FOR A FIXED WING ACFT. IT SEEMED TO ME AND MY PHOTOGRAPHER THAT HE ALMOST WANTED TO ATTACK US. IN FACT; HE WAS FLYING VERY CLOSE AND LOW TOWARD US. THAT HAD ALSO THE EFFECT THAT HE FORCED US MORE OR LESS TO A LOWER ALT; PLUS HE INCREASED THE NOISE LEVEL IN THAT AREA EVEN MORE. AT THAT TIME; I HEARD HIM TALKING TO THE LCL SHERIFF HELI. HE TOLD THEM THAT I WAS FLYING RECKLESSLY 10 FT OVER HOUSES; WHICH IS JUST NOT TRUE. I LEFT THE AREA IMMEDIATELY AND THE GUY IN THE C152 FOLLOWED US TO PETALUMA; CA. WE LANDED AND PARKED THE HELI AT PETALUMA ARPT (O69) ON THE RAMP. A FEW MINS LATER; I SAW THE CESSNA TAXIING BEHIND US ON THE TXWY. HE DIDN'T STOP NOR DID HE TALK TO US AND THEN HE LEFT.