# Presentation: 498609

## Mapping Terrestrial Water and Carbon fluxes using AMSR-E and MODIS 

**John Kimball****1,2**

- 1Numerical Terradynamic Simulation Group, University of Montana, USA.
-  2Flathead Lake Biological Station, Division of Biological Sciences, Univ. MT.

**Joint AMSR Science Team Meeting; July 14-16 2008 **

- _with_: Lucas Jones1,2, Ke Zhang1,2 and Qiaozhen Mu1

## Slide 2

## Recent Changes to Pan-Arctic Water/Carbon Budgets

**Recent Changes to Pan-Arctic Water/Carbon Budgets**

**1**Kang et al., 2008. *J. Geophys. Res*.; 2007. **2***Geophys Res. Lett*. 34, L21403

## Remote Sensing of Land-Atmosphere C Exchange

- GPP

- Tmult

- Wmult

- Scalar Multipliers (DIM)

- Decomp. Rates (d-1)

- Flux Calc. (kg C m-2):

- C Substrate Pools (kg C m-2)

- Rh = (Kmet * Cmet + Kstr + Cstr + Krec * Crec)

- Cmet = Cfract * NPP
- Cstr = (1-Cfract) * NPP
- Crec = 0.7 * Cstr

- Kmet = (Kmx * Tmult * Wmult)
- Kstr = 0.4 * Kmet
- Krec = 0.01 * Kmet

- Tsoil (deg C)

- 1*Soil Moisture (% Sat.)

- Land cover (BPLUT)

**(AMSR-E)**

**(MODIS)**

- NPP = GPP * (1-CUE)
- Ra = GPP - NPP

- Cfract
- CUE

- Rh – NPP = **NEE**

**SOC** = (Cmet + Cstr + Crec) - **R****h**

- Outputs:

- Inputs:

**Remote Sensing of Land-Atmosphere C Exchange**

_**1**_Njoku, E.G.  (2004).  AMSR-E/Aqua Daily L3 Surface Soil Moisture, V001, *NSIDC*, Boulder, CO, USA. Digital Media
- * Scaled between max-min observations

## Daily Surface Soil Temperature Retrieval from AMSR-E

- Daily surface (<10cm depth) soil temperature retrievals (in degrees Celsius) using AMSR-E multi-frequency brightness temperatures; Remote sensing results are plotted against MODIS LST and site level measurements of soil temperature (Tsoil) and minimum daily air temperature (Tmin) from boreal forest and tundra monitoring sites.

**Daily Surface Soil Temperature Retrieval from AMSR-E**

- _Source_: Jones et al., 2007.*Trans. Geosci. Rem. Sens.* 45(7).

## MODIS-AMSR-E Carbon Model Results

- RMSE [g C m-2 d-1] accuracy relative to Tower Obs: 0.8-1.8 (GPP); 0.4-0.9 (Rtot); 0.6-1.7 (NEE)

**MODIS-AMSR-E Carbon Model Results**

## Carbon Model Error Sensitivity

**Carbon Model Error Sensitivity**

- _Source_: Kimball et al. 2008. *Trans. Geosci. Rem. Sens*. (in press)
**2**Baldocchi, D., 2008. *Australian Journal of Botany* 56.

- Estimated carbon model RMSE uncertainty from MODIS (**1**GPP) and AMSR-E (Ts and SM) inputs indicates MODIS/AMSR-E accuracies (GPP~1.2 g C m-2 d-1; Ts < 3.5 K; SM < 40 % [~20 % vol]) sufficient to resolve NEE to within ~7-31 g C m-2 yr-1. This is within the **1**reported (30-100 g C m-2 yr-1) range of accuracy for tower measurements.

*1**Assumed constant GPP error of 1.2 g C m**-2** d**-1**; average GPP = 500 g C m**-2** y**-1*

**SM = 30 % Sat**

**Tsoil = 10 °C**

## Estimating ET from MODIS-AMSR-E Inputs

**Estimating ET from MODIS-AMSR-E Inputs**

## Satellite Based Daily ET Algorithm Flow Chart

**Satellite Based Daily ET Algorithm Flow Chart**

- _Source:_** **Mu, Q. et al., 2007. Rem. Sens. Environ. 111.

**MODIS**

**GMAO**

- Model
- _Inputs_

## Vegetation Biomass Constraints on Microwave RS Observations of Soil Processes

- 1Veg. Water Content/Roughness [kg m-2]

- 1 Frequency dependence of canopy loss from Njoku & Chan *Rem. Sens. Environ. *(2006)

**Vegetation Biomass Constraints on Microwave RS Observations of Soil Processes**

**Notes:**
Iterative inversion of an RT Tb model that represents the pixel as a mix of open water and dry, vegetated land.  H and V polarizations from 6.9, 10.7, 18.7, and 35.6 GHz Tb’s were used.  Scene is for  July 9, 2003.    

## Linear correlation between AMSR-E uncorrected Tbv values for various frequencies and in situ temperature measurements for selected tundra (HPV), grassland (LTH) and boreal forest (NOBS, OAS) sites.

- _Source_: Jones et al., 2007.*Trans. Geosci. Rem. Sens.* 45(7).

## Daily Air Temperature (Tmn, Tmx, Tav) Estimation from AMSR-E day/night Tbs

**Daily Air Temperature (T****mn****, T****mx****, T****av****) Estimation from AMSR-E day/night T****b****s**

- Method 1:  Multiple Regression
- Uses vertically polarized AM/PM (Asc/Desc)Tb data at 10.7, 18.7, and 89 GHz frequencies, and H/V polarization ratios of the 6.9 GHz and 89 GHz channels
- Method 2: Emissivity Triangle RT-model

- Each pixel represents a mixture of open water and vegetated soil:

- Uses 6.9, 10.7, 18.7, 36.5 GHz polarization ratios to iteratively solve for open water fraction and vegetation/roughness parameters and uses 36.5 GHz V-pol. AM/PM Tbs to solve for Tmn/Tmx

## Estimating Daily Vapor Pressure Deficit

- Uses AMSR-E Tmx/Tmn retrievals to calculate mean daily air temperature
- Assumes Tmn = Dewpoint temperature1
- Relatively Robust for northern regions with low night-time temperatures and high surface water storage (low surface evaporative resistance)
- An arid region correction can be applied1

- _1__Source:_ Kimball et. al. *Ag. For. Meteor.* (1997) 85.

- Tmn

- Tmx

- VPD

- kPa

- °C

- July 9, 2003

## Comparison of AMSR-E and GMAO meteorological variables to tower observations at all sites; solid lines represent the linear least-square regression line, while dashed lines represent a 1:1 relationship. 

- Comparison of AMSR-E and GMAO meteorological variables to tower observations at all sites; solid lines represent the linear least-square regression line, while dashed lines represent a 1:1 relationship.

- _Source_: Mu, Q. et al., 2008.*Water Resources. Research* (In-review).

##  Tower vs Model Based ET

** ****Tower vs Model Based ET**

- _Source_: Mu, Q. et al., 2008.*Water Resources. Research* (In-review).

- Mean Annual ET

## RS-ET Error 1Sensitivity

- Absolute error (solid black lines; W/m2) and relative error (dashed gray lines; %) propagated to model derived latent energy flux (LE) for three error levels of AMSR-E derived air temperatures. Meaningful LE information is derived when LE > 7-26 W/m2 (ET > 0.13 – 1.33 mm/d) given observed MODIS/AMSR-E input and model uncertainty. Meteorological inputs contribute 28-65% of total model LE error and translate to ~3-7% relative error in cumulative ET over a 100-day growing season.

**RS-ET Error ****1****Sensitivity**

**1**LAI, dew point temperature, net incoming solar radiation, and error in net incoming solar radiation are held at constant, moderate values of 3 m2 m-2, 0 °C, 300 W/m2, and 70 W/m2 (~20%), respectively.  Tmax varies from 0 to 30 °C.  Soil evaporation is considered negligible.

- _Source_: Mu, Q. et al., 2008.*Water Resources. Research* (In-review).

## Results Summary

** ****AMSR-E T****b**** data provide reasonable estimates of surface Ta and VPD across wide range of surface/climate conditions; results similar to or better than alternative measures from station corrected reanalysis (GMAO) meteorology; **
** ****Use of MODIS GPP and AMSR-E Tsoil, SM within a simple carbon model captures regional patterns and variability SOC stocks and C-fluxes relative to site measurements and ecosystem model simulations. Model results within range of tower measurement error;**
** **
** ****MODIS-AMSR-E based ET results similar to tower measurements and alternate results using local and reanalysis (GMAO) based daily meteorology; **
** ****Processing of these data continues from 2002-present and spans all Northern Hemisphere vegetated land areas; **
** ****Results provide basis for assessing northern carbon-water cycle interactions and ecosystem response to recent warming.**

## Slide 18

## Back-up Slides

## Model Development and Validation Sites

**Model Development and Validation Sites**

## Carbon Model Results Comparison over Tower Sites

**Carbon Model Results Comparison over Tower Sites**

## Relations Between TCF and BIOME-BGC Based Annual Carbon Fluxes

**Relations Between TCF and BIOME-BGC Based Annual Carbon Fluxes**

## Slide 23

**Notes:**
Iterative inversion of an RT Tb model that represents the pixel as a mix of open water and dry, vegetated land.  H and V polarizations from 6.9, 10.7, 18.7, and 35.6 GHz Tb’s were used.  Scene is for  July 9, 2003.    

## AMSR-E Daily 1Soil Moisture Retrievals

**AMSR-E Daily ****1****Soil Moisture Retrievals**

**NSA-OBS, **
**CN (ENLF)     **

**Barrow, AK **
**(Coastal Tundra)   **

**Lethbridge, CN (Grassland)**

**Site vs. AMSR-E SM for Tower Windows**

**Scaled L3 product**
**June 15,**
** ****2003**

- AMSR-E soil moisture RMSE values range from 22 to 48 %; R2 range 0.59 to  <0.01 for both methods.
- AMSR-E results similar to site (BIOME-BGC) modeled soil moisture accuracy (RMSE range from 22 to 44 %; R2 range 0.53 to  <0.01).
- Retrieval error increases primarily under increasing biomass and water fraction

_**1**__Source_: Njoku, E.G.  (2004).  AMSR-E/Aqua Daily L3 Surface Soil Moisture, V001, *NSIDC*, Boulder, CO, USA. Digital Media
- * Scaled between max-min observations

**Surface Wetness % Sat**

## Multiple regression method: 

**Multiple regression method: **

**Emission Process method: **

- Uses normalized polarization ratio [      = (*Tbv *-*Tbh*)/(*Tbv *+*Tbh*)] to correct for surface water
- Multiple V-pol. bands (6, 10, 23, 89 GHz) contribute additional information; separate coefficients for frozen and non-frozen conditions.

- Assumes each pixel represents a mixture of open water and vegetated soil
- Slope (a) and intercept (b) dependence on land surface emissivity described  by simple RT equation  and constant open water emissivity
- Iterative minimization of Ts for adjacent bands allows simultaneous estimates of land emissivity and Ts.

- _Source_: Jones, L.A., et al., 2007. *Trans. Geosci. Rem. Sens*. 45(7), 2004-2018.

## Seasonality in MODIS Based ET 

**Seasonality in MODIS Based ET **

- _Source_: Mu, Q. et al., 2008.*Water Resources. Research* (In-review).

## MODIS-AMSR-E Estimated Surface Soil Organic Carbon 

**MODIS-AMSR-E Estimated Surface Soil Organic Carbon**** **
**(≤10cm depth, 2002-2004)**

- TCF = MODIS-AMSR-E C model
- BGC = BIOME-BGC
- IGBP-DIS = Global SOC Inventory
- Site = Tower site SOC Inventory