ICESAT-2 SCIENCE DEFINITION STUDIES TO MEASURE FOREST STRUCTURE THIS PROPOSAL RESPONDS TO ICESAT AND CRYOSAT PROGRAM OF NASA ROSES-2011 CALL FOR THE RECOMPLETE OF THE ICESAT-2 SCIENCE DEFINITION TEAM. THIS PROPOSED ACTIVITY ADDRESSES A PRIMARY ISSUE REGARDING THE APPROPRIATE USE OF ICESAT-2 PHOTON-COUNTING LIDAR DATA FOR CRITICAL CARBON CYCLE AND ECOSYSTEM MEASUREMENTS. AT THIS POINT, THE ICESAT-2 ENGINEERING DESIGN IS ESTABLISHED ALTHOUGH STILL SUBJECT TO MINOR MODIFICATION. NASA EXPECTS TO LAUNCH A 6-BEAM, 1 K HERTZ, 10M FOOTPRINT, 40M IFOV, PHOTONCOUNTING MICROPULSE LIDAR WITH 3 PAIRED, 0.532 UM WAVELENGTH, WEAK/STRONG BEAMS 25 UJ AND 100 UJ - IN 2016. GIVEN THESE SYSTEM ATTRIBUTES, WE WILL SEEK TO DEVELOP ONE OR MORE ALGORITHMS USING BEST AVAILABLE SIGNAL-PROCESSING TECHNOLOGY THAT WILL IDENTIFY THE GROUND SIGNAL, TOP-OF-CANOPY, AND INTERMEDIATE FOREST CANOPY RETURNS WITHIN DATA LIMITATIONS IMPOSED BY (D.1) AMBIENT ATMOSPHERIC CONDITIONS, (D.2) DATA ACQUISITION TIME (I.E., DAY VERSUS NIGHT), (D.3) SIGNAL TO NOISE RATIO, (D.4) BEAM STRENGTH, (D.5) LOCAL/REGIONAL TOPOGRAPHIC CONDITIONS, (D.6) FOREST CANOPY DENSITY, AND (D.7) GROUND SURFACE REFLECTANCE. THE TEAM WILL UTILIZE SIMULATED ICESAT-2 DATA ACQUIRED BY THE ER2-MABEL AIRBORNE INSTRUMENT WHICH ACQUIRES PHOTON-COUNTING OBSERVATIONS THROUGH 90% OF THE EARTH S ATMOSPHERIC COLUMN. ALGORITHMS DEVELOPED BY THIS NASA/TAMU/DUKE TEAM WILL BE COMPARED TO PROCEDURES DEVELOPED BY OTHER ICESAT-2 VEGETATION TEAM MEMBERS WITH THE IDEA THAT THE BEST ATTRIBUTES OF ALL ALGORITHMS WILL BE INTEGRATED TO PRODUCE THE PROGRAM(S) NEEDED TO POST-PROCESS GLOBAL, TERRESTRIAL ICESAT-2 DATA. EXPECTED RESULTS INCLUDE (R.1) THE DEVELOPMENT OF ALGORITHMS DESIGNED TO EXTRACT GROUND AND FOREST CANOPY SIGNALS FROM AMBIENT PHOTON NOISE, (R.2) AN ASSESSMENT OF THE ACCURACY OF THESE ALGORITHMS WITH RESPECT TO ESTIMATING FOREST CANOPY HEIGHT AND CANOPY CLOSURE BY COMPARING ALGORITHM RESULTS WITH GROUND PLOT, TERRESTRIAL LIDAR, AND AIRBORNE LIDAR MEASUREMENTS, (R.3) THE USE OF THESE SIMULATED ICESAT-2 HEIGHT AND CANOPY CLOSURE METRICS TO PREDICT FOREST BIOMASS AND CARBON AND TO ASSESS THE ACCURACY/PRECISION OF THESE ESTIMATES BY COMPARING PREDICTED ESTIMATES TO GROUND MEASUREMENTS, AND (R.4) THE DEFINITION OF THE D.1-D.7 LIMITS WITHIN WHICH THESE ICESAT-2 METRICS AND ESTIMATES CAN BE MEASURED/PREDICTED. EXPECTED RESULT R.4 IS NOTABLE IN THAT, USING SIMULATED ICESAT-2 DATA OBTAINED FROM A HIGH-ALTITUDE AIRBORNE PHOTON COUNTING LASER (MABEL), WE WILL IDENTIFY, FOR THE WEAK AND STRONG BEAMS, (1) CANOPY CLOSURE LIMITS ABOVE WHICH GROUND SIGNALS CANNOT BE RELIABLY RETRIEVED BENEATH DENSE FOREST CANOPIES AND (2) CANOPY CLOSURE LIMITS BELOW WHICH CANOPY HEIGHTS CANNOT BE RETRIEVED DUE TO THE SHORT STATURE OR LOW STEM DENSITY OF THE FOREST CANOPY. THE RESULTS FROM THIS PROPOSED INVESTIGATION WILL HELP PROVIDE DATA GLOBALLY THAT CAN BE USED TO ADDRESS SEVERAL IMPORTANT QUESTIONS POSED BY NASA S EARTH SCIENCE ENTERPRISE INCLUDING: WHAT IS THE CURRENT STATE OF GLOBAL FOREST RESOURCES? HOW ARE GLOBAL ECOSYSTEMS CHANGING? WHAT ARE THE CONSEQUENCES OF LAND COVER AND LAND USE CHANGE? HOW IS THE EARTH S SURFACE BEING TRANSFORMED AND HOW CAN SUCH INFORMATION BE USED TO PREDICT FUTURE CHANGES?