Using MISR to Map Woody Plant Canopy Crown Cover, Height, and Biomass Mark Chopping1, John V. Martonchik2, Michael Bull2, Gretchen G. Moisen3, Ron Tymcio3, Barry (Ty) Wilson4, and Albert Rango5 1 Earth & Environmental Studies, Montclair State University, Montclair, NJ 2 NASA/JPL, Pasadena, CA 3 USDA, Forest Service Rocky Mountain Research Station, Ogden, UT 4 USDA, Forest Service Northern Research Station, St. Paul, MN 5 USDA, ARS Jornada Experimental Range, New Mexico State University, Las Cruces, NM.
The Simple Geometric-optical Model (SGM) predicts top-of-canopy bidirectional reflectance as a function of viewing and illumination angles and Arizona and New Mexico Forest important canopy parameters: plant number density, mean crown radius, mean crown aspect ratio, mean crown center height ratio, and background reflectance magnitude and anisotropy. The model was adjusted against red band data in nine views from the Multiangle Imaging SpectroRadiometer The southwestern forest maps (Fig. 9) were produced by merging data from nine Terra overpasses using model fitting error as the compositing (MISR) on the NASA Earth Observing System Terra satellite to retrieve estimates of crown cover, mean canopy height, and woody biomass (via criterion, removing clouds. 1063 random forest locations were used to extract MISR/SGM retrievals and the corresponding data from Forest regression) on a 250 m grid for large parts of Arizona and New Mexico. A first test of the applicability of this method to northeastern forests was Service maps for the Interior West, based on FIA and other data. Filtering on high model fitting RMSE, a few outliers, and screening for also examined at two scales: at Howland Forest and for a large part of the state of Maine (Terra orbit 013824). For the SW forests, the background topographic shading reduced N to 576 (Fig. 10). The height retrievals were consistent with data from the FS height map (Table 1, Fig. 11, angular response in the MISR viewing plane was estimated prior to model inversion using the isotropic, geometric, and volume scattering weights of bottom). These results show that MISR data can be interpreted through a simple GO model to provide maps of canopy crown cover, canopy a LiSparse-RossThin kernel-driven model, plus nadir camera blue, green and near-infrared reflectance, with calibration obtained using the SGM with height, and biomass over large areas of the southwes tern US that are highly compatible with US Forest Service data (Chopping et al. 2008a). plant mean radius and number density estimates obtained from Ikonos panchromatic imagery. For the NE forests, a fixed background bidirectional MISR/GO Regional Woody Plant MISR/GO Regional Woody reflectance distribution function was used owing to lack of calibration data. In both cases, the mean crown center height ratio, crown foliage density, 100 km Fig. 9 N Aboveground Biomass Plant Mean Canopy Height leaf reflectance, and tree number density were fixed at typical values and fractional crown cover and canopy height calculated by adjusting crown Fig. 10 radius (exploiting sensitivity to brightness) and crown aspect ratio (exploiting sensitivity to reflectance factor shape). A sequence of crown cover and canopy height retrievals for 2000-2007 was also effecte d for desert grasslands in New Mexico in order to assess retrievals over this period. Howland Forest & Maine MISR/SGM canopy height and crown cover retrievals for Howland Forest show a spatial match with H100 heights from the Lidar Vegetation Imaging Sensor (LVIS) in the range 10.0-30.0 m, although there is a compression of the MISR height estimates to a range of 7-19 m (Fig. 1). The 0.00 6.70 >50.0 (a) (b) (c) 2 Tons/ acre < 1.00 relationship is relatively weak (R =0.21) but positive. The cover estimates (range: 0.0 - 0.8) are more noisy than the height estimates. Height and 0.00 15.0 >110.0 1.00 >20.00 Mg ha-1 cover estimates are lower for roads and areas with few trees. In view of the lack of background calibration, the heterogeneity of the landscape, and meters MISR/GO Regional Woody US Forest Service Estimated the fixing of model parameters, these results are deemed promising. Figure 2 (a) and (c) show MISR/SGM canopy height and crown cover retrievals Plant Fractional Crown Cover Biomass on Hillshaded Elevation for parts of Maine alongside Forest Service maps produ ced using a nearest-neighbor imputation method that exploits Forest Inventory Analysis (FIA) Table 1 Fractional Mean canopy Woody Biomass crown cover height -1 -1 data Fig. 2 (b) and (d). Only one MISR orbit was used; data missing owing to surface or aerosol retrieval failures are shown in grey. There is a (tons acre ) (Mg ha ) (dimensionless) (meters)
spatial correspondence between the height maps (MISR range: 10-30 m) but the MISR/SGM cover estimates (range: 0.3-0.6) show an anomalous Sevilleta Mean Relative Error (% ) 3 0 2 8 2 8 -
distribution with respect to the Forest Service stocking % map, used here as a proxy for crown cover. These results are not unexpected in view of Mean Absolute Error 0 . 1 0 2 . 2 4 . 5 1 0 . 1
the lack of background calibration and the fixing of model parameters. Mean (MIS R ) 0 . 4 8 1 0 . 3 2 1 . 8 4 9 . 0
Mean (USFS) 0 . 3 8 8 . 7 2 1 . 8 0 . 0 Arizona Root Mean Square Error 0 . 1 2 3 . 3 6 . 2 1 4 . 0 0.00 0.29 Jornada roads streams lakes Shrubs New Mexico R2 0 . 7 8 0 . 6 9 0 . 8 1 - 0.30 0.90 Forest 30.0 50 km y = 1.0069x + Bright white = anomalies 0.1162 Source: USFS-IWFIA Map 2 < 6 > 60 25.0 R = 0.2117 Biomass (tons/acre)
20.0
15.0
10.0 New Mexico Desert Grassland
MISR/SGM Mean Canopy Height (m) 5.0
0.0 A sequence of SGM inversions using a dynamic background was performed using MISR scenes for May-June of 2000-2007 for the area in New 0.0 5.0 10.0 15.0 20.0 25.0 30.0 LVIS/H100 Canopy Height (m) Mexico bounding the USDA, ARS Jornada Experimental Range and the NWS Sevilleta National Wildlife Refuge. Woody plant mean radius and crown aspect ratio were adjustable, allowing mapped estimates of crown cover and canopy height to be obtained (Fig. 12 (a)-(b)). This approach was used to map forest with some success (Chopping et al. 2008a) but previous studies in grasslands had allowed only cover as the Fig. 1: (a) LVIS H100 Canopy Heights (b) MISR/SGM Height (c) Aerial Orthophoto (d) MISR/SGM Crown Cover (e) MISR/SGM Height Estimates (f) MISR vs LVIS Hgt (rescaled) adjustable parameter (Chopping et al. 2008c, d). These preliminary results -- with no screening for the quality of the model fitting or cloud contamination -- are impacted by inter-annual variability in precipitation and the use of background coefficients from 2002. Since the modeling framework attempts to isolate the contribution from the soil-understory background prior to estimating the contribution from shrubs and trees, spikes in understory growth owing to precipitation result in changes to the structure and scattering properties of the background, even after senescence. Unusually large rainfall events prior to the 2005, 2006, and 2007 acquisitions are likely the reason for the anomalous retrievals for those years, and particularly 2005 and 2007 (Fig. 12 (d-9), (e)). Although it is clear from these results that measurement precision for shrubs is low when both cover and height are adjustable, the maps for all years show similar spatial structure. These results highlight the challenge of remotely measuring shrub cover and height under conditions in which the background is dynamic in both sp ace and time.
(a) crown cover (b) canopy height 1: JER-shrubs-West 2: Tarbush-N. of JER 3: Low cover North of 4: JER-Creosotebush 5: SEV-Creosotebush 6: SEV-Juniper White Sands -East -West Woodlands
(c) 350 m2
Figure 2 Canopy Height: (a) MISR/SGM (b) Forest Service Figure 2 Crown Cover: (c) MISR/SGM (d) FS % Stocking 7: Low shrub cover -- 8: JER-shrubs-E 9: JER-bare 10: JER-Mesquite 11: JER-Black Grama 12: JER-playa College Ranch Dunes grassland
(d) (1) (2) (3) (4) (5) (6) Figure 2 Detail (Height): (e) MISR/SGM (f) Forest Service Figure 2 Detail (Cover): (g) MISR/SGM (h) FS % Stocking
Arizona and New Mexico Forest: Comparison with Forest Inventory Analysis Survey Data (7) (8) (9) (10) (11) (12)
40.0 1.00 100.00 All relationships were positive but correlations between the MISR/SGM- 0.80 2 30.0 estimated and FIA height, cover, and biomass values were low, with R in 0.60 (a) 20.0 (b) (c) 50.00 the ranges 0.29–0.42, 0.23–0.57, and 0.43–0.55, respectively, amongst 0.40
10.0 all the data sets. In general biomass was better estimated than canopy 0.20 (1) (2) (3) (4) (5) (6) MISR/SGM Crown Cover MISR/SGM Biomass (t/acre) 2 2 MISR/SGM Canopy Height (m) R2 = 0.3706 R = 0.235 R = 0.4676 0.0 0.00 0.00 height or crown cover; and canopy height better than crown cover. 0.0 10.0 20.0 30.0 40.0 0.00 0.20 0.40 0.60 0.80 1.00 0.00 50.00 100.00 FIA Weighted Height (m) FIA Crown Cover FIA Biomass (t/acre) MISR/SGM crown cover values diverged from the FIA value far more than Figure 3. Filters: Month = All, Year = All; Plot Design = 1 (N = 1589) canopy height for all data sets except the 2005 and 2001-2003 subsets. 40.0 1.00 100.00 The best mean absolute error results were obtained for the “all data” set:
0.80 30.0 -1 3.3 meters in height, 0.21 in fractional cover, and 10.81 tons acre in (7) (8) (9) (10) (11) (12) 0.60 Fig 12. (above, right) MISR/SGM (a) crown (a) 20.0 (b) (c) 50.00 biomass. Differences in means (MISR/SGM estimates minus FIA) were 0.40 cover and (b) height maps for 2002 (c) high -1 10.0 low: <=0. 4 meters, <=0.2, and <=2.5 tons acre . For the May-Sept resolution images, sites 1-12, (d) retrieved 0.20 MISR/SGM Crown Cover
MISR/SGM Biomass (t/acre) cover and height vs previous year’s precipitation 2 2 2 MISR/SGM Canopy Height (m) R = 0.3364 R = 0.2436 R = 0.4488 2002 set where both evergreen and deciduous species are in leaf, 0.0 0.00 0.00 (e) daily precipitation. Fig. 13 (below) Mapped 0.0 10.0 20.0 30.0 40.0 0.00 0.20 0.40 0.60 0.80 1.00 0.00 50.00 100.00 FIA Weighted Height (m) FIA Crown Cover FIA Biomass (t/acre) correlation coefficients were higher, with mean absolute errors of 4.0 m, retrievals for playa (site 12) (a) crown cover (b) -1 mean canopy height (c) high resolution image. Figure 4. Filters: 4 < Month < 10, Year = All; Plot Design = 1 (N = 593) 0.20, and 11.6 tons acre , respectively. The disparity in scale is thought (e) Precipitation 40.0 1.00 100.00 to be an important source of divergence between the MISR and FIA data Terra orbit used 0.80 30.0 sets; the extent of an FIA plot is small compared to the MISR ground- (a) (b) (c) 0.60 (a) 20.0 (b) (c) 50.00 projected instantaneous field-of-view (GIFOV; Fig. 8). Moreover, tree 0.40
10.0 MISR/SGM (t/acre) measurements are made only at the four sub-plots and there is no 0.20 MISR/SGM Crown Cover
2 2 2 MISR/SGM Canopy Height (m) R = 0.4214 R = 0.4017 R = 0.457 indication of landscape spatial heterogeneity within plots. 0.0 0.00 0.00 0.0 10.0 20.0 30.0 40.0 0.00 0.20 0.40 0.60 0.80 1.00 0.00 50.00 100.00 FIA Weighted Height (m) FIA Crown Cover FIA Biomass (t/acre) Figure 5. Filters: 4 < Month < 10, Year = 2002; Plot Design = 1 (N = 28) (a) (b) 40.0 1.00 100.00
0.80 30.0 Multiangle reflectance factors from MISR were interpreted through an hybrid geometric-optical model. In an heterogeneous, managed boreal 0.60 (a) 20.0 (b) (c) 50.00 0.40 forest at Howland, Maine using a fixed background, the relationships with LVIS canopy height, roads, rivers, and clearcuts are obvious. Over a
10.0 0.20
MISR/SGM Crown Cover large part of Maine using the same fixed background matches with Forest Service maps were less consistent. However, using a dynamic 2 2 MISR/SGM Biomass (t/acre) 2 MISR/SGM Canopy Height (m) R = 0.3594 R = 0.5679 R = 0.5454 0.0 0.00 0.00 0.0 10.0 20.0 30.0 40.0 0.00 0.20 0.40 0.60 0.80 1.00 0.00 50.00 100.00 background obtained a priori to map woody plant distributions (crown cover, mean canopy height, and aboveground woody biomass) for large FIA Weighted Height (m) FIA Crown Cover FIA Biomass (t/acre) parts of Arizona and New Mexico, good agreements with Forest Service maps and positive relationships with the FIA survey data were obtained. Figure 6. Filters: 4 < Month < 10, Year = 2005 (N = 17) 40.0 1.00 100.00 For desert grasslands in New Mexico, temporal stability in preliminary, unscreened retrievals over 2000-2007 was impacted by inter-annual
0.80 30.0 variation in precipitation and the use of background coefficients obtained for a single year. (a) 0.60 20.0 (b) (c) 50.00 0.40 Chopping, M., Moisen, G. Su, L., Laliberte, A., Rango, A., Martonchik, J.V., and Peters, D.P.C. (2008a), Large area mapping of southwestern forest crown cover, canopy height, and biomass using MISR, Remote 10.0 0.20 Sens. Environ., 112: 2051-2063.
MISR/SGM Crown Cover 250 meters
2 MISR/SGM Biomass (t/acre) MISR/SGM Canopy Height (m) R2 = 0.2925 R = 0.3522 R2 = 0.4283 Chopping, M. (2008b), Terrestrial Applications of Multiangle Remote Sensing, in: Advances in Land Remote Sensing: System, Modeling, Inversion and Applications, S. Liang, ed., Springer- Verlag, 95-144. 0.0 0.00 0.00 0.0 10.0 20.0 30.0 40.0 0.00 0.20 0.40 0.60 0.80 1.00 0.00 50.00 100.00 Chopping, M., Su, L., Rango, A., Martonchik, J.V., Peters, D.P.C., and Laliberte, A. (2008c), Remote sensing of woody shrub cover in desert grasslands using MISR with a geometric-optical canopy reflectance FIA Weighted Height (m) FIA Crown Cover FIA Biomass (t/acre) Figure 8. (a) FIA Plot Design (b) FIA plot in relation to a 250 m2 raster cell. Note that the FIA plot model, Remote Sens. Environ. 112: 19-34 Figure 7. Filters: 4 < Month < 10, Year = 2001-2003 (N = 83) might be located anywhere within the cell. Chopping, M., Su, L., Laliberte, A., Rango, A., Peters, D.P.C., and Martonchik, J.V. (2006), Mapping woody plant cover in desert grasslands using canopy reflectance modeling and MISR data, Geophsyical Research Letters 33, L17402, doi:10.1029/2006GL027148.
40.0 Figure 11. Plot of filtered, random reference points, Arizona and New Mexico 30.0
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0.0 1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 113 120 127 134 141 148 155 162 169 176 183 190 197 204 211 218 225 232 239 246 253 260 267 274 281 288 295 302 309 316 323 330 337 344 351 358 365 372 379 386 393 400 407 414 421 428 435 442 449 456 463 470 477 484 491 498 505 512 519 526 533 540 547 554 561 568 575 Sample #
NASA Carbon Cycle & Ecosystems Joint Workshop, Adelphi, MD, April 28-May 2, 2008. Acknowledgments: This work was supported by NASA grant NNG04GK91G to MC. Thanks: David Diner, J. Bryan Blair, K. Jon Ranson, and Guoqing Sun. Data credits: NASA/JPL,LARC/ASDC, US Forest Service, NASA/GSFC Laser Remote Sensing Lab., climate data: John Anderson, USDA, ARS, Jornada Experimental Range. WWW: http://csam.montclair.edu/~chopping/wood