diff --git a/include/gridpp.h b/include/gridpp.h
index c65183c..eccd691 100644
--- a/include/gridpp.h
+++ b/include/gridpp.h
@@ -293,23 +293,22 @@ namespace gridpp {
             int max_points,
             bool allow_extrapolation=true);
 
-    /** Optimal interpolation for an ensemble gridded field (alternative version). This is an experimental method.
-      * @param bgrid Grid of background field
+    /**Optimal interpolation for an ensemble gridded field with ensemble-based correlations. The function supports iterative corrections to the analysis. Each ensemble member is adjusted iteratively or "ensemble member by ensemble member" (ebe).
+      * @param bgrid Grid of background field 
       * @param bratios 2D vector (Y, X) of the ratio of background error standard deviation at grid points to that at observation points.
       * @param background 3D vector (Y, X, E) representing the background values at grid points to be updated.
       * @param background_corr 3D vector (Y, X, E) representing the background values used to compute dynamic correlations.
-      * @param obs_points observation points. S = num. observations
-      * @param pobs 2D vector of perturbed observations (S, E)
+      * @param obs_points Observation points (S = num. observations)
+      * @param pobs 2D vector of perturbed observations (S, E) 
       * @param pratios 1D vector (S) of the ratio of observation to background error variance.
       * @param pbackground 2D vector (S, E) representing the background values at observation points used to compute innovations.
       * @param pbackground_corr 2D vector (S, E) representing the background values at observation points used to compute dynamic correlations.
-      * @param structure Structure function
+      * @param structure Structure function for the localization function
       * @param max_points Maximum number of observations to use inside localization zone; Use 0 to disable
-      * @param dynamic_correlations Determines whether to use flow-dependent correlations derived from the ensembles. If true, the structure function defines localization functions. If false, the structure function defines static (non-flow-dependent) correlations.
       * @param allow_extrapolation Allow EnSI to extrapolate increments outside increments at observations
       * @returns 3D vector of analised values (Y, X, E)
     */
-    vec3 optimal_interpolation_ensi_multi(const Grid& bgrid,
+    vec3 optimal_interpolation_ensi_multi_ebe(const Grid& bgrid,
             const vec2& bratios,
             const vec3& background,
             const vec3& background_corr,
@@ -320,7 +319,58 @@ namespace gridpp {
             const vec2& pbackground_corr,
             const StructureFunction& structure,
             int max_points,
-            bool dynamic_correlations=true, 
+            bool allow_extrapolation=true); 
+
+    /** Optimal interpolation for an ensemble gridded field with static correlations. The function supports iterative corrections to the analysis.
+      * @param bgrid Grid of background field 
+      * @param bratios 2D vector (Y, X) of the ratio of background error standard deviation at grid points to that at observation points.
+      * @param background 3D vector (Y, X, E) representing the background values at grid points to be updated.
+      * @param obs_points Observation points (S = num. observations)
+      * @param pobs 2D vector of perturbed observations (S, E) 
+      * @param pratios 1D vector (S) of the ratio of observation to background error variance.
+      * @param pbackground 2D vector (S, E) representing the background values at observation points used to compute innovations.
+      * @param structure Structure function for the correlation function
+      * @param max_points Maximum number of observations to use inside localization zone; Use 0 to disable
+      * @param allow_extrapolation Allow EnSI to extrapolate increments outside increments at observations
+      * @returns 3D vector of analised values (Y, X, E)
+    */
+    vec3 optimal_interpolation_ensi_multi_ebesc(const Grid& bgrid,
+            const vec2& bratios,
+            const vec3& background,
+            const Points& obs_points,
+            const vec2& pobs,
+            const vec& pratios,
+            const vec2& pbackground,
+            const StructureFunction& structure,
+            int max_points,
+            bool allow_extrapolation=true); 
+
+    /** Optimal interpolation for an ensemble gridded field with ensemble-based correlations. The function supports iterative corrections to the analysis. First, "use (and adjust) the ensemble mean" (utem), then generate the analysis ensemble.
+      * @param bgrid Grid of background field 
+      * @param bratios 2D vector (Y, X) of the ratio of background error standard deviation at grid points to that at observation points.
+      * @param background 3D vector (Y, X, E) representing the background values at grid points to be updated.
+      * @param background_corr 3D vector (Y, X, E) representing the background values used to compute dynamic correlations.
+      * @param obs_points Observation points (S = num. observations)
+      * @param pobs 1D vector of observations (S)
+      * @param pratios 1D vector (S) of the ratio of observation to background error variance.
+      * @param pbackground 2D vector (S, E) representing the background values at observation points used to compute innovations.
+      * @param pbackground_corr 2D vector (S, E) representing the background values at observation points used to compute dynamic correlations.
+      * @param structure Structure function for the localization function
+      * @param max_points Maximum number of observations to use inside localization zone; Use 0 to disable
+      * @param allow_extrapolation Allow EnSI to extrapolate increments outside increments at observations
+      * @returns 3D vector of analised values (Y, X, E)
+    */
+    vec3 optimal_interpolation_ensi_multi_utem(const Grid& bgrid,
+            const vec2& bratios,
+            const vec3& background,
+            const vec3& background_corr,
+            const Points& obs_points,
+            const vec& pobs,
+            const vec& pratios,
+            const vec2& pbackground,
+            const vec2& pbackground_corr,
+            const StructureFunction& structure,
+            int max_points,
             bool allow_extrapolation=true); 
 
     /** Optimal interpolation for an ensemble point field with ensemble-based correlations. The function supports iterative corrections to the analysis. Each ensemble member is adjusted iteratively or "ensemble member by ensemble member" (ebe).
@@ -380,7 +430,7 @@ namespace gridpp {
       * @param bratios 1D vector (L) of the ratio of background error standard deviation at grid points to that at observation points.
       * @param background 2D vector (L, E) representing the background values at grid points to be updated. 
       * @param obs_points Observation points (S = num. observations)
-      * @param pobs 2D vector of perturbed observations (S, E)
+      * @param pobs 1D vector of observations (S)
       * @param pratios 1D vector (S) of the ratio of observation to background error variance.
       * @param pbackground 2D vector (S, E) representing the background values at observation points used to compute innovations.
       * @param structure Structure function for the static correlations
diff --git a/src/api/oi_ensi_multi.cpp b/src/api/oi_ensi_multi.cpp
index df6fde5..5339d4d 100644
--- a/src/api/oi_ensi_multi.cpp
+++ b/src/api/oi_ensi_multi.cpp
@@ -30,18 +30,18 @@ void print_matrix(Matrix matrix) {
 template void print_matrix< ::mattype>(::mattype matrix);
 template void print_matrix< ::cxtype>(::cxtype matrix);
 
-vec3 gridpp::optimal_interpolation_ensi_multi(const gridpp::Grid& bgrid,
+// ensemble member by ensemble member (ebe)
+vec3 gridpp::optimal_interpolation_ensi_multi_ebe(const gridpp::Grid& bgrid,
         const vec2& bratios,
         const vec3& background, 
         const vec3& background_corr, 
         const gridpp::Points& points,
         const vec2& pobs,
-        const vec& pratios, 
+        const vec& pratios,
         const vec2& pbackground, 
         const vec2& pbackground_corr,
         const gridpp::StructureFunction& structure,
         int max_points,
-        bool dynamic_correlations,
         bool allow_extrapolation) {
     double s_time = gridpp::clock();
 
@@ -69,12 +69,12 @@ vec3 gridpp::optimal_interpolation_ensi_multi(const gridpp::Grid& bgrid,
     int nE = background[0][0].size();
     if(background.size() != nY || background[0].size() != nX) {
         std::stringstream ss;
-        ss << "Input left field (" << background.size() << "," << background[0].size() << "," << background[0][0].size() << ") is not the same size as the grid (" << nY << "," << nX << "," << nE << ")";
+        ss << "Input background field (" << background.size() << "," << background[0].size() << "," << background[0][0].size() << ") is not the same size as the grid (" << nY << "," << nX << "," << nE << ")";
         throw std::invalid_argument(ss.str());
     }
     if(background_corr.size() != nY || background_corr[0].size() != nX || background_corr[0][0].size() != nE) {
         std::stringstream ss;
-        ss << "Input LEFT field (" << background_corr.size() << "," << background_corr[0].size() << "," << background_corr[0][0].size() << ") is not the same size as the grid (" << nY << "," << nX << "," << nE << ")";
+        ss << "Input background_corr field (" << background_corr.size() << "," << background_corr[0].size() << "," << background_corr[0][0].size() << ") is not the same size as the grid (" << nY << "," << nX << "," << nE << ")";
         throw std::invalid_argument(ss.str());
     }
     if(bratios.size() != nY || bratios[0].size() != nX) {
@@ -84,12 +84,12 @@ vec3 gridpp::optimal_interpolation_ensi_multi(const gridpp::Grid& bgrid,
     }
     if(pbackground.size() != nS || pbackground[0].size() != nE) {
         std::stringstream ss;
-        ss << "Input right field at observation location (" << pbackground.size() << "," << pbackground[0].size() << ") and points (" << nS << "," << nE << ") size mismatch";
+        ss << "Input pbackground field at observation location (" << pbackground.size() << "," << pbackground[0].size() << ") and points (" << nS << "," << nE << ") size mismatch";
         throw std::invalid_argument(ss.str());
     }
     if(pbackground_corr.size() != nS || pbackground_corr[0].size() != nE) {
         std::stringstream ss;
-        ss << "Input RIGHT field at observation location (" << pbackground_corr.size() << "," << pbackground_corr[0].size() << ") and points (" << nS << "," << nE << ") size mismatch";
+        ss << "Input pbackground_corr field at observation location (" << pbackground_corr.size() << "," << pbackground_corr[0].size() << ") and points (" << nS << "," << nE << ") size mismatch";
         throw std::invalid_argument(ss.str());
     }
     if(pobs.size() != nS || pobs[0].size() != nE) {
@@ -119,12 +119,96 @@ vec3 gridpp::optimal_interpolation_ensi_multi(const gridpp::Grid& bgrid,
         }
     }
     vec2 output1 = gridpp::init_vec2(nY * nX, nE); 
-    if(dynamic_correlations) {
-        output1 = optimal_interpolation_ensi_multi_ebe(bpoints, bratios1, background1, background_corr1, points, pobs, pratios, pbackground, pbackground_corr, structure, max_points, allow_extrapolation);
+    output1 = optimal_interpolation_ensi_multi_ebe(bpoints, bratios1, background1, background_corr1, points, pobs, pratios, pbackground, pbackground_corr, structure, max_points, allow_extrapolation);
+    vec3 output = gridpp::init_vec3(nY, nX, nE);
+    count = 0;
+    for(int y = 0; y < nY; y++) {
+        for(int x = 0; x < nX; x++) {
+            for(int e = 0; e < nE; e++) {
+                output[y][x][e] = output1[count][e];
+            }
+            count++;
+        }
     }
-    else {
-        output1 = optimal_interpolation_ensi_multi_ebesc(bpoints, bratios1, background1, points, pobs, pratios, pbackground, structure, max_points, allow_extrapolation);
+    return output;
+} // end optimal_interpolation_ensi_multi_ebe
+
+// ensemble member by ensemble member with static correlations (ebesc)
+vec3 gridpp::optimal_interpolation_ensi_multi_ebesc(const gridpp::Grid& bgrid,
+        const vec2& bratios,
+        const vec3& background, 
+        const gridpp::Points& points,
+        const vec2& pobs,
+        const vec& pratios,
+        const vec2& pbackground, 
+        const gridpp::StructureFunction& structure,
+        int max_points,
+        bool allow_extrapolation) {
+    double s_time = gridpp::clock();
+
+    // Check input data
+    if(max_points < 0)
+        throw std::invalid_argument("max_points must be >= 0");
+
+    int nS = points.size();
+    if(nS == 0)
+        return background;
+
+    int nY = bgrid.size()[0];
+    int nX = bgrid.size()[1];
+
+    if(nY == 0 || nX == 0) {
+        std::stringstream ss;
+        ss << "Grid size (" << nY << "," << nX << ") cannot be zero";
+        throw std::invalid_argument(ss.str());
     }
+
+    if(bgrid.get_coordinate_type() != points.get_coordinate_type()) {
+        throw std::invalid_argument("Both background grid and observations points must be of same coordinate type (lat/lon or x/y)");
+    }
+    // Check ensembles have consistent sizes
+    int nE = background[0][0].size();
+    if(background.size() != nY || background[0].size() != nX) {
+        std::stringstream ss;
+        ss << "Input background field (" << background.size() << "," << background[0].size() << "," << background[0][0].size() << ") is not the same size as the grid (" << nY << "," << nX << "," << nE << ")";
+        throw std::invalid_argument(ss.str());
+    }
+    if(bratios.size() != nY || bratios[0].size() != nX) {
+        std::stringstream ss;
+        ss << "Input bratios field (" << bratios.size() << "," << bratios[0].size() << ") is not the same size as the grid (" << nY << "," << nX << ")";
+        throw std::invalid_argument(ss.str());
+    }
+    if(pbackground.size() != nS || pbackground[0].size() != nE) {
+        std::stringstream ss;
+        ss << "Input pbackground field at observation location (" << pbackground.size() << "," << pbackground[0].size() << ") and points (" << nS << "," << nE << ") size mismatch";
+        throw std::invalid_argument(ss.str());
+    }
+    if(pobs.size() != nS || pobs[0].size() != nE) {
+        std::stringstream ss;
+        ss << "Observations (" << pobs.size() << "," << pobs[0].size() << ") and points (" << nS << "," << nE << ") size mismatch";
+        throw std::invalid_argument(ss.str());
+    }
+    if(pratios.size() != nS) {
+        std::stringstream ss;
+        ss << "Ratios (" << pratios.size() << ") and points (" << nS << ") size mismatch";
+        throw std::invalid_argument(ss.str());
+    }
+ 
+    gridpp::Points bpoints = bgrid.to_points();
+    vec2 background1 = gridpp::init_vec2(nY * nX, nE);
+    vec bratios1(nY * nX);
+    int count = 0;
+    for(int y = 0; y < nY; y++) {
+        for(int x = 0; x < nX; x++) {
+            bratios1[count] = bratios[y][x];
+            for(int e = 0; e < nE; e++) {
+                background1[count][e] = background[y][x][e];
+            }
+            count++;
+        }
+    }
+    vec2 output1 = gridpp::init_vec2(nY * nX, nE); 
+    output1 = optimal_interpolation_ensi_multi_ebesc(bpoints, bratios1, background1, points, pobs, pratios, pbackground, structure, max_points, allow_extrapolation);
     vec3 output = gridpp::init_vec3(nY, nX, nE);
     count = 0;
     for(int y = 0; y < nY; y++) {
@@ -136,7 +220,110 @@ vec3 gridpp::optimal_interpolation_ensi_multi(const gridpp::Grid& bgrid,
         }
     }
     return output;
-}
+} // end optimal_interpolation_ensi_multi_ebesc
+
+// use the ensemble mean (utem)
+vec3 gridpp::optimal_interpolation_ensi_multi_utem(const gridpp::Grid& bgrid,
+        const vec2& bratios,
+        const vec3& background, 
+        const vec3& background_corr, 
+        const gridpp::Points& points,
+        const vec& pobs,
+        const vec& pratios,
+        const vec2& pbackground, 
+        const vec2& pbackground_corr,
+        const gridpp::StructureFunction& structure,
+        int max_points,
+        bool allow_extrapolation) {
+    double s_time = gridpp::clock();
+
+    // Check input data
+    if(max_points < 0)
+        throw std::invalid_argument("max_points must be >= 0");
+
+    int nS = points.size();
+    if(nS == 0)
+        return background;
+
+    int nY = bgrid.size()[0];
+    int nX = bgrid.size()[1];
+
+    if(nY == 0 || nX == 0) {
+        std::stringstream ss;
+        ss << "Grid size (" << nY << "," << nX << ") cannot be zero";
+        throw std::invalid_argument(ss.str());
+    }
+
+    if(bgrid.get_coordinate_type() != points.get_coordinate_type()) {
+        throw std::invalid_argument("Both background grid and observations points must be of same coordinate type (lat/lon or x/y)");
+    }
+    // Check ensembles have consistent sizes
+    int nE = background[0][0].size();
+    if(background.size() != nY || background[0].size() != nX) {
+        std::stringstream ss;
+        ss << "Input background field (" << background.size() << "," << background[0].size() << "," << background[0][0].size() << ") is not the same size as the grid (" << nY << "," << nX << "," << nE << ")";
+        throw std::invalid_argument(ss.str());
+    }
+    if(background_corr.size() != nY || background_corr[0].size() != nX || background_corr[0][0].size() != nE) {
+        std::stringstream ss;
+        ss << "Input background_corr field (" << background_corr.size() << "," << background_corr[0].size() << "," << background_corr[0][0].size() << ") is not the same size as the grid (" << nY << "," << nX << "," << nE << ")";
+        throw std::invalid_argument(ss.str());
+    }
+    if(bratios.size() != nY || bratios[0].size() != nX) {
+        std::stringstream ss;
+        ss << "Input bratios field (" << bratios.size() << "," << bratios[0].size() << ") is not the same size as the grid (" << nY << "," << nX << ")";
+        throw std::invalid_argument(ss.str());
+    }
+    if(pbackground.size() != nS || pbackground[0].size() != nE) {
+        std::stringstream ss;
+        ss << "Input pbackground field at observation location (" << pbackground.size() << "," << pbackground[0].size() << ") and points (" << nS << "," << nE << ") size mismatch";
+        throw std::invalid_argument(ss.str());
+    }
+    if(pbackground_corr.size() != nS || pbackground_corr[0].size() != nE) {
+        std::stringstream ss;
+        ss << "Input pbackground_corr field at observation location (" << pbackground_corr.size() << "," << pbackground_corr[0].size() << ") and points (" << nS << "," << nE << ") size mismatch";
+        throw std::invalid_argument(ss.str());
+    }
+    if(pobs.size() != nS) {
+        std::stringstream ss;
+        ss << "Observations (" << pobs.size() << ") and points (" << nS << ") size mismatch";
+        throw std::invalid_argument(ss.str());
+    }
+    if(pratios.size() != nS) {
+        std::stringstream ss;
+        ss << "Ratios (" << pratios.size() << ") and points (" << nS << ") size mismatch";
+        throw std::invalid_argument(ss.str());
+    }
+ 
+    gridpp::Points bpoints = bgrid.to_points();
+    vec2 background1 = gridpp::init_vec2(nY * nX, nE);
+    vec2 background_corr1 = gridpp::init_vec2(nY * nX, nE);
+    vec bratios1(nY * nX);
+    int count = 0;
+    for(int y = 0; y < nY; y++) {
+        for(int x = 0; x < nX; x++) {
+            bratios1[count] = bratios[y][x];
+            for(int e = 0; e < nE; e++) {
+                background1[count][e] = background[y][x][e];
+                background_corr1[count][e] = background_corr[y][x][e];
+            }
+            count++;
+        }
+    }
+    vec2 output1 = gridpp::init_vec2(nY * nX, nE); 
+    output1 = optimal_interpolation_ensi_multi_utem(bpoints, bratios1, background1, background_corr1, points, pobs, pratios, pbackground, pbackground_corr, structure, max_points, allow_extrapolation);
+    vec3 output = gridpp::init_vec3(nY, nX, nE);
+    count = 0;
+    for(int y = 0; y < nY; y++) {
+        for(int x = 0; x < nX; x++) {
+            for(int e = 0; e < nE; e++) {
+                output[y][x][e] = output1[count][e];
+            }
+            count++;
+        }
+    }
+    return output;
+} // end optimal_interpolation_ensi_multi_utem
 
 // ensemble member by ensemble member (ebe)
 vec2 gridpp::optimal_interpolation_ensi_multi_ebe(const gridpp::Points& bpoints,